I commend tanks when I see them adjust to changing situations appropriately and actively try to maintain enmity when they lose it suddenly to a burst DPS.

I commend healers who can keep paper tanks alive through the worst of situations and can manage big pulls fluidly.

I commend DPS that know how to maintain their own entity while still maximizing their DPS and performing well.

It's all situational and having switched from PLD to BRD, I still do get comms routinely, it's just not as many. But then, I don't mind since I've already completed all the comm achievements.