"We're team "C", I'll be in the vicinity of "C" and if you're out of range you'll probably die" - My Void Ark battle cry, but it still doesn't stop half the party from being over at "A" all fight.

Outside of that sort of scenario, it's really situational in my experience. In AS1 I was finding I basically took 2 DPS and a tank and my co healer did the same, and I'd just drop an Aspected Benefic (Diurnal) on his tank now and again.