On the original question, I'd say only allow it if you feel it will be appropriate to your campaign. You have to make a judgment based on a balance of several issues: player desires, campaign identity, minmaxing concerns, etc.
If your players are going to use it to min-max, and you don't want that in your campaign, then I'd recommend against allowing it. If that is the only reason, I'd make sure they actually
are going to min-max, though. Some players who are completely capable of min-maxing are also completely willing not to. As long as they are willing to respect your wishes, it isn't necessarily true that multiclassing = min-maxing.
If multiclassing messing with your sense of your campaign world and makes it unsatisfying for you, then I would recommend disallowing it. An unhappy DM is an unhappy group.
Personally, I think multiclassing can be used for desirable or undesirable reasons. In my campaigns a class is about fluff as much as about crunch. I allow multiclassing, and I don't even require you to jump through hoops of training time or extensive justification for it (no offense to those who do). But I do require all character concepts to fit my campaign, and my campaigns often have certain character parameters. Being a fighter or a wizard, or whatever, means you have had the training and identified with that class. It isn't a set of powers you can refluff to create a new custom class. If you are dipping for a power combo first, and trying to justify it second, I'm going to discourage that. On the other hand if your concept involves two classes, and you just happen to decide whether you want 4 or 5 levels in one of them based on what feature you will get out of it, that's fine. You already planned a character who included significant investment in that class identity, you are just fine tuning it with rules awareness.
In general, it seems to me that 1-2 levels of any class is usually a min-maxing dip first, role-playing second--although there might be exceptions.
On the other hand trying to more or less evenly split your levels as you progress is almost always a strong story-driven character concept, and it almost never makes a character more powerful. More often than not, it weakens a character. In AD&D/hybrid style multiclassing, where you choose your classes at level 1 and are stuck with them, multiclassing is also very likely to be a character concept choice instead of a power-gaming choice.
Just kinda wondering (because I play in pro Multiclassing Groups) what some of you guys think about this:
This will allow me to develop some of my philosophy on the issues, so I'll go ahead and comment on how I would handle this as your DM.
I want to play a Holy Warrior of the Good Dragon God.
Okay, sounds good. I'm going to assume we are in a fairly typical traditional D&D world. Ie, Greyhawk or Forgotten Realms (1e-3e eras), and I tend to ignore the more gonzo aspects of 3e Forgotten Realms. If that doesn't fit your idea of a campaign setting you are on board with, none of this will be relevant to you. However, were I your DM, I would have told you about the campaign world before I invited you to make a character, so we'll assume you're on board for the purposes of this commentary.
The Good Dragon God is going to be Bahamut, unless you are interested in one of the lesser draconic deities. We can go over them and see which ones you like. Since you are a humanoid, this is a rather odd option and we'll have to work out why you worship a draconic god in your backstory. Dwarves don't have a racial hatred of dragons, so it won't be hard to justify, but it will take some approval.
I start out as a Mountain Dwarf Warlock with the Good Dragon being my patron (use the Arch Devil from the PHB).
Say whaaaat?
Okay, so you are a dwarf who worships a draconic deity. Well, that's certainly more difficult than being one of those crazy eclectic humans. Dwarves are a lot more culturally normalized and don't tend to run across every spectrum like it's going out of style, so you're draconic deity worshipping dwarf is already problematic. Not insurmountable, but you are setting yourself up as a weirdo, and we'll have to discuss it and see why he has this sort of religious inclination, and what sort of clan he comes from and where his sanity is sitting, etc.
Now...warlock? Dwarf warlock? This is where I "call you into my office" and ask you to explain to me why you brought a dwarf warlock to work. It's pretty darn far out there.
Take 5 levels of Warlock- Get to 2nd attacks
Then take 2 levels of Paladin to get the SMITE ability
Then take the the rest of the levels in SORCERER to gain more spell to convert to smites
Okay, so this is highly mechanically focused, and I'm probably going to reject it on that basis. I'll work with you and see if your character concept (story-driven) came first and you are just trying to create it mechanically, or if it were the other way around. Let's assume you really liked the character concept and that just seemed like the best way to manifest it in the rules.
From the concept you described, forget about warlock. Too much of a stretch and doesn't fit a good draconic deity. It also seems rather unnecessary for your concept.
Paladin I can do. So let's just start as a paladin--that's the class defined as a holy warrior, and you wanted to be a holy warrior. It's also a class that works well story-wise for dwarves. Now you are a dwarf who for some backstory reason really connected with Bahamut and his teachings, and decided to be a holy crusader in service of his causes. A bit eccentric, but sounds acceptable.
Now you are thinking of taking sorcerer levels (I'm assuming draconic). If the only reason is to get more spell slots for smiting, that is a no. If the primary reason is to get more spell slots for smiting, and you are thinking up ways to justify it in the story, it is still probably a no. If, on the other hand, you always saw this dwarf having a sorcerous arcane streak, I'll start discussing it with you. Why do you feel a need to add sorcerer to his story? I can see how you might look at it as providing a connection with your deity--but paladin or cleric really doesn't need any added connection. Providing an additional kind of connection is redundant and unnecessary.
But perhaps you want some arcane dragony magic--it just feels like he should have it. Okay, let's consider taking the Magic Initiate feat, and take draconic as one of your languages. Or perhaps you'd prefer the Ritual Caster feat, or perhaps both. That will allow you to add some arcane spice.
The character from start to finish is a front line fighter who fights in the name of his god.
Stick with paladin.
Just wondering, why wouldn't some of you allow this? Why would you just prefer the PC be a straight Paladin or Fighter or Cleric?
Yes, I would prefer that. I'd also find out whether your concept is primarily that of a holy
warrior or that of a
priest who fights. The former is a paladin and the latter is a cleric.
Also, at some point in our discussion, I would find out if you are actually okay with the changes and requirements I'm imposing on your character, or if you'd be more comfortable just playing an entirely different character in this campaign. If it is frustrating you because you honestly have a really exotic character concept that doesn't fit my setting, I'm not going to frustrate us both trying to fit it. I'm just going to say that it would fit better in another campaign, and we should look at a different character for this campaign. It could be a similar character, say you mostly just want a dwarf tank and are fine with a dwarf paladin of Moradin or cleric (War domain) of Clangeddin. Problem solved. Or perhaps you will save that idea for a different campaign, and play the half-elf rogue aristocrat you've been considering. Problem solved. I firmly believe that almost anyone has multiple character concepts that they can enjoy playing--some people just need a bit of help figuring out what those are.
I'll also note that I'm assuming my own campaign and my own setting (including my own take on a published setting), and that I come up with campaign ideas before I invite players. I tell you what my campaign is and you decide whether it works for you. If you say it works for you, then I approve or disapprove your character based on whether it works for my campaign. If I couldn't find enough people to play in a specific campaign then I wouldn't run that campaign right then. My players approve my campaign by signing on to play, and I approve their character or ask them create another one. Mutual approve, individual creative control. I would only come up with a campaign idea in concert with the players if we were going to be having a shared DMing campaign (which is cool).
Of course, if we are playing Lost Mine of Phandelver or some other disconnected one-shot adventure I'd probably just let you play whatever you want.
