I've always found multiclass "dipping" purely for mechanical benefit and without story justification to be incredibly lame. Which is why it never happens at my tables. If any players feel like they want/need some game mechanic that can only be found in some other class, I have no problem with just doing feature swaps so they can have it. A Cleric wants a Fighting Style? Absolutely, I'll give them a fighting style in exchange for one of their other features. A Paladin wants a ranged spell cantrip because it fits their character theme? No problem, we'll make a switch.
But if you are going to multiclass, especially at the beginning of your character career, then I'm expecting you to pretty much split levels evenly between the two classes. And if you voluntarily do that because it is a part of your character's story? Then I'll be appreciative and probably still give you your "character level" abilities like Extra Attack or your ASIs at your proper character level anyway. Because game mechanics are just numbers and I can balance them relatively easily-- both between PCs and between the PCs and the game world. So I'm not going to be a stickler for where/when/how you get game mechanics... I'm much more concerned about your PC's story and how balanced the STORY is in the world and between other PCs.
But if you are going to multiclass, especially at the beginning of your character career, then I'm expecting you to pretty much split levels evenly between the two classes. And if you voluntarily do that because it is a part of your character's story? Then I'll be appreciative and probably still give you your "character level" abilities like Extra Attack or your ASIs at your proper character level anyway. Because game mechanics are just numbers and I can balance them relatively easily-- both between PCs and between the PCs and the game world. So I'm not going to be a stickler for where/when/how you get game mechanics... I'm much more concerned about your PC's story and how balanced the STORY is in the world and between other PCs.