Depends on the feats. Depends on the player. Depends on the build.
EX: when I make characters, when they're human, they're often some kind of pirate theme (I dunno, I think humans play this trope best) but they'll almost always take Magic Initiate, why? Because I want a parrot! It's still a good feat. I'm probably not putting it to the best use.
But for some specific responses....
Actor Feat: "You can mimic the speech of another person or the sounds made by other creatures. You must have heard the person speaking, or heard the creature make the sound, for at least 1 minute. A successful Wisdom (Insight) check contested by your Charisma (Deception) check allows a listener to determine that the effect is faked."
Without this feat in the game, why wouldn't you be able to try a Charisma (Deception) check to try and mimic the speech of another person or sound made by other creatures, contested by a Wisdom (Insight) check? And if Player X has this feat in your game, wouldn't it be natural for a DM to tell Player Y they cannot try that because they don't have the feat and it would step on the toes of Player X who spent a precious resource to gain that "ability"?
The feat puts the burden on the listener. Without the feat it goes like this:
Bob: I try to imitate the Guard Captain.
DM: Okay make your check
Bob: *16* Is it believable?
DM: *results*
In this situation, Bob has to make the attempt to
sound like the subject. With the feat it goes like this:
Bob: I imitate the Guard Captain, "i'm busy! Go away!"
DM: *rolls check for NPC*
The feat switches where the burden is placed. With the feat, it is
on the listenerto determine there is something afoot.
: "You can spend 10 minutes inspiring your companions, shoring up their resolve to fight. When you do so, choose up to six friendly creatures (which can include yourself) within 30 feet o f you who can see or hear you and who can understand you. Each creature can gain temporary hit points equal to your level + your Charisma modifier. A creature can’t gain temporary hit points from this feat again until it has finished a short or long rest."
Without this feat in the game, if a Player makes a very inspiring speech which the DM judges would give a psychological boost to their allies, the DM might choose to give those allies some temporary hit points from the speech related to the PC's charisma (and probably would limit it to those who could hear it rather than an arbitrary 30' distance). They might even allow it a second time without as rest, under appropriate circumstances (like a forced march while chasing foes who have kidnapped their companion). But with this feat in the game if Player X has it, it would be hard for a DM to justify allowing Player Y to try it, or to even alter the rules to have it work without a short rest or outside 30' because the rule is right there in black and white on a PC's character sheet that way.
In short, the DM can do whatever the frell he wants. You can make an inspiring speech and the DM can turn all the listeners into chickens (literally). You can stand on one foot while reciting poetry and attempting to pat your head and rub your belly and the DM can say that gravity just reversed.
If your argument
against the feat is that "Well the DM could just set up some checks and make the thing happen anyway!"
Well yeah the DM
can do that. But then WTF do we need rules for if we're just going to have the DM make everything up?
Rules are what keeps the game from being Calvinball. I don't want to play D&D Calvinball.
: "You always know which way is north. You always know the number of hours left before the next sunrise or sunset. You can accurately recall anything you have seen or heard within the past month."
Without this feat in the game, any of these things could be determined with an appropriate ability/skill check, or perhaps even automatically depending on the circumstances. And maybe it still could even with this feat in the game. However, if Player X happens to have this feat? The DM will probably naturally feel more reluctant to hand out that sort of information without the feat to the other PCs who lack it.
There was an entire thread on this. Maybe reading it would provide good insight? The key word here is "always".
: "You can ably create written ciphers. Others can’t decipher a code you create unless you teach them, they succeed on an Intelligence check (DC equal to your Intelligence score + your proficiency bonus), or they use magic to decipher it."
Without this feat in the game, I see no reason why any PC couldn't try and create a written cipher which could be broken by an Intelligence check similar to the one described. With it, I can see a DM having trouble justifying allowing such a thing without the feat.
Again, the DM can do whatever he darn tootin pleases.
Okay. I'm done.
Literally EVERY argument you just made was "Well the DM could have called for rolls and made something up!"
Well yes. He could. He could make everything up. We could toss the book aside, I mean who need class features that tell you how many attacks you get? The Dm could just call for a check! Who needs to know how much damage a longsword does? The Dm could just call for a check!
You see my point here?