it's too situational to make a general rule about in or out of the circle. solo healer i'd never go into the circle even with my stats spent on vit and full vit acc. 2 healers one in one out is better than both in usually but not always. if the second healer didnt join as healer and just switched, has low hp, he probably can't be counted on in wich case 2 out might be better. 3 healers all 3 in always i'd say, but i'm sure a situation where that's not best could be pointed out to me.

to the op just play how you think is best. if someone is telling you to do something you think is stupid... don't do it. if you're never in the circle you're probably not always doing the right thing, if you're always in the circle you're definitely not always doing the right thing.