
Her_Lotho |

I'm always of the opinion that everyone at my table should play whatever they want to play if:
a) It's balanced.
b) Their characters back-story makes sense for the adventure at hand. And personally i think the players guides do a great job of providing inspiration to the players to explain how their character of race X and class Y can fit into the campaign. "If you can explain it, you can play it", is my idea.
I don't think in general it's a good idea to enforce your players to play something just because you think they might need a character of class X or class Y would be better for balance. It's always the quirky parties that are the most fun to have imo. And i find that in general players will find original ways to make their group composition work for them. And if they don't seem to cope, you as a dm can always provide them with some help by making some tweaks to the adventure (eg such as changing the loot tables to better suit their needs).
And if you confine them to certain classes, you should really allow them to fill in that class as they wish and select their own feats. Players need to feel invested in their character to make the most out of it. You can of course provide them with plenty of background information and hints to what they might face in the campaign. Such as eg. there will be a fair share of undead to aid them in their choices. It's better to gently nudge them towards a choice then to enforce it.;)