Playing Baldur's gate I always ran 6 in my party, needed someone to take abuse, learn scrolls, heal, melee damage, range, and general support. 2nd editions rules kinda demanded it if you didn't want to miss out.

All that said I would prefer NOT to have 6 members in the party because the forced diversity simply isn't there. I can have my wizard/cleric heal/ranged dps (still getting used to wizard being able to heal) if I need a tank fighter or cleric covers it, ranged physical dps can be covered by fighter, ranger, rogue. Lock picking and trap disarming can really go to anyone with a decent sex score so far so each character really brings with it a lot more value with it.

The other thing to consider is that the original games rewarded exp according to party size and 3 is kinda built in a milestone fashion.

Really at the end of the day you're only limited by your creativity. I've run comps with no healer just fine (especially with food all over the place and short rests)