I often give comms but certainly as hell do not get in return for many instances even if going out of my way like raising other players on my Red Mage because a healer is either dead or too focused on using StoneIV and i do Mana Shift also.
It is a completely optional thing however and some times i do feel like i wish i can give more then the 1 person a comm, but i think many people just do not care.