I sometimes restrict or eliminate spellcasting classes if overt magic use is inappropriate for the world (which, to be fair, it usually is). Psionics, variant magic systems (M&M powers, say) and other systems I actually like tend to be more thematically appropriate, by some strange chance...
I don't think I've ever banned or restricted a fighting class, though.
I've banned races due to world appropriateness. Usually, I run either Spelljammer (no restrictions of any kind, if not incentives to play something oddball) or human-only with perhaps a few more 'monstrous' races available at higher levels.
I've never banned a published feat.
I've never banned a published prestige class. Even spellcasting ones; they're usually appropriate by the time PCs have access to them.
I actively pass around non-WotC books (Arcana Evolved, DragonMech, Iron Kingdoms, OGL Steampunk, etc.) and d20 Modern books, encouraging players to use options from them.
I've never banned a book from play although a no-dwarves, no-gnomes, no-goliaths campaign has little use for, say,
Races of Stone. Couldn't care less if I own the books the players use or not.
I
would ban some combinations for balance reasons (Punpun, Cheater of Mystra, etc.), but none have ever come up that I didn't allow.