There is a minor debate in the FFXIV community as to the proper way to play healers in random groups. FFXIV healing is not super-spammy. If you heal efficiently, you often have several free GCDs. So many good healers add damage during those free GCDs, as damage spells cost very little mana. Indeed, edge healers learn to go into the damage stance (Cleric stance - reduces healing, increases damage) at appropriate times in order to maximize the amount of damage they can do.
This has led to a discussion of the role of healers in random groups. Should you expect the healer in a random group to add damage? Or is a healer who solely heals--as is normal in many other MMOs--acceptable?
This in turn encouraged some good healers conduct experiments on random groups. They did several runs maximizing damage, while still keeping everyone alive. Then they did several runs where they did no damage, and just focused on keeping people topped off. Universally, it's been found that the pure healing runs yield more commendations from the other party members. This implies that the FFXIV community prefers the pure healing style.
This has caused some consternation among the edge healers. Why does the FFXIV community not recognize the optimum play-style?
I think that the answer is more psychological than anything else. In a random group, you don't know how much you can trust the unknown healer. So a healer who doesn't deal damage, but does keep everyone topped off creates a feeling of safety. That gives the other group members confidence and makes life easier for them.
Aggressively dealing damage as a healer generally means letting people drop in health a bit, and not topping them off right away. With an unknown healer, this can be a bit nerve-wracking for the other party members. Is the healer actually bad, and going to let someone die? Do I need to play more defensively to compensate?
So the best way to get commendations as a healer in random groups is to make your group feel utterly safe, and allow them to enjoy a smooth run without concern. In a group where everyone knows and trusts each other, this is not the best way to play. But in a random group, generating trust is often more important than strict performance.