I main BLM, but play all of the jobs, and quite frequently heal. I actually played healer for Coil 2, when it was the current raid, rather than BLM since I enjoyed healing it. Even when that content was considered difficult I still spent part of my time contributing to dps. That said, I understand certain situations where healers exclusively heal.

If I'm healing, I generally like to contribute as much as possible. So if I'm in Ex Roulette, for example, and on WHM (since it's the only healer lvl 60 I have at the moment), I always start my "rotation" with the tank picking up a mob or two, followed by me popping regen, maybe a cure (if needed), Aero 3, another cure (if needed), then a holy to stun the enemies that can get stunned. Then I go back to healing the tank or start popping DoTs on individual enemies. Eventually I rinse and repeat. If the enemies are going down slowly, and I'm able to, I'll start throwing out Stone 3....all depends on how much damage the tank is taking at any given time.

When I heal I like to be productive 24/7, whether it's healing or dpsing. I just adjust to the needs of the party.

If I'm in a particular run where the tank is squishy, or simply doesn't like to use defensive CDs, then I notice myself in more of a mana drain, so I might only pop at least an aero 3 to get something on the mobs, but will then conserve my MP to make sure I can keep the tank up in case of large hits etc.

In general, though, I am usually able to do a lot of dps even when the party is a bit squishy or the content is more difficult. Like I said before, even when Coil 2 was new, I would still pop some dps in between heals whether I was playing WHM or SCH. It all depends on comfort level, I guess. I'm also not afraid to use benediction (when playing WHM) if we're doing a huge pull of enemies, and I still want to throw out some attacks.

If I'm tanking and barely taking damage, I do get semi annoyed when the healer is standing there doing absolutely nothing for a good 5-10 seconds...I will admit that gets a bit on my nerves, but at the same time, I would never call someone out on it or make a big deal of it. Just more of my mind thinking "why is that healer just standing around doing nothing, and he/she has full mp?"