I think, like most others, thereās a difference between banning for power, and banning for story.
At VALUE:
For power: No, thatās why we have VALUE rules.
For story: I can see doing this, although I havenāt had occasion yet. Much like everything weāve already seen with the evil or Dragonborn sessions, it gives people the chance to experience something different. So communication ahead of time, and I thought @Darthbinks bringing the pre-gens is a nice way of helping out players who might not be able to prep.
In Campaigns:
For power:
Classes/subclasses, no. Because it doesnāt solve the problem. If someone wants to power game, theyāre going to do it, Iām not going to read dozens of books to try to stop them. I think as the others described, itās better to work with the player to achieve the right balance within the party, and if needed tone things done on an individual level with agreement from the player. So long as the party agrees with what level of strength theyāre aiming for (a Tomb of Horrors party may be differently balanced than a standard one), then itās not an issue.
I will say this: Iāve learned that a party doesnāt need to be completely balanced in combat. Maybe even āshouldnātā be. It took me awhile to learn that as a DM. Characters are more than their damage output. Ideally, each character in a campaign has their own strength, whether itās combat (ranged or melee), stealth, intelligence, jack-of-all-trades, or whatever. In one event, maybe the strongest combat player shines. But maybe in the next one, they have to hold the line against the big evil monster, but the actual most important thing is that rogue who has to make balance checks to get across the beam to reach the artifact. Or the high intelligence scholar who has to quickly decipher the script to banish the demon (did I just slip into Cthulu? Sorry). As long as each person in the party believes they have their own role to play, it works out.
For Story: Yes, I have, to make for a better story for players. Since itās conveyed before players ever make characters, Iāve never really had anyone fight too hard against it. Probably because itās done to make for a better story for the players, not for a DMās personal amusement. Re: Krynn, if I was running that era as a campaign, Iād ask for no clerics/paladins for that purpose.