There's a school of thought I've run into more than once that healers don't have to be as aware of timers as DPS and tanks because they should be staring at bars. I have to say, perhaps my perspective is unique as I've only really been raiding in 25 man content for less than a year now, and I have since learned how to communicate in vent.
I know, it sounds so simple--just push the button and talk, right?--but there are lots of ways to communicate well and many more ways to communicate poorly. I remember trying to help my man RL 10 man raids, and complaining to him about all the things that people weren't doing, as they weren't doing them, yet I would refuse to just open my vent channel and say "please switch to the kobolds ASAP" or "remember to move the fire away from the raid" or "phase transition, get ready to run". I was, and still am, afraid of being the Bitch.
I'd like to think I've gotten better. It took getting to know the group I played with, and learning that sometimes I really do need to impart information right now. I call out timers. I remind the raid that stuff on the ground is coming up or to get ready for the big fear. I announce my status: I say "Enlynn's valked, big heals on the tank" or "Enlynn's dropping stacks, big heals on the tank" or "Enlynn's silenced, big heals on the tank" (recurring theme here, yes?).
I struggled with calling out my status for a long time. I don't wish to be perceived as self-important, but tank healing and tanking are the most communication-sensitive parts of the game. It's a natural thing to coordinate tank-swaps, adds, debuff management, and anything else that endangers the tanks. It's the first check of the game, keeping the tanks alive to soak the beating. Healers and damage dealers come second.
(I'm not suggesting that tanks and healers and damage dealers are more or less valuable in a group. Tanks are a single point of failure in an encounter, we won't get to the enrage timer if the tanks can't stay alive to see it).
Part of tank healing is not hps or gear or skill, it's reliability. It's not very exciting that our peers are talking about hypothetical damage per second, set bonuses, and pew pew, while I'm maximizing... my reliability factor. How many times have I been incapacitated by an encounter mechanic and thought I didn't need to call it out on vent, only to have the tank go splat because, get this, no one knew to help me heal.
How many wipes could I have prevented if I just pushed the button and said "big heals on the tank"?
There's another huge upside to learning to communicate with the team. My silence means that all is going well. If I want the raid healers to trust me to heal the tank, I really do want to call it out when I can't, otherwise we have three raid healers twitching tank heals because they can't trust me to ask for help when I need it. If they trust me, they can focus on what they need to do, knowing that if I get unchained magic, frost beaconed, or sucked into the sword, I'll ask them to heal the tank.
In a pug, it's even more important. Assuming that the raid leader is paying attention can be a dangerous mistake. I joined a pug LK10 last week, and I unabashedly called out each time I needed help. It covers my ass. If I'm asking for heals on the tank and the tank dies, I did the best I could do and I am not the only one to blame. If I ask for heals on the tank and the tank lives, I've saved us from a wipe. Was it actually necessary? It's hard to say, if they other healers were good they saw it on their raid frames that I was valked or in the dream or in the sword, and were adjusting before I called it out. But again, that's making some pretty serious assumptions.
I'm not an expert on when to call out and when not to. I'm sure that I've called out the most unnecessary things, while keeping my mouth shut when I shouldn't have. Most of the time, it wouldn't wipe the raid if I didn't (or would it?). It's not a chance I want to take. I'll call it out just in case.
I'm sure half the raid thinks "ugh I wish she would just shut up sometimes", but they can deal. I'm not trying to be self-important, I'm trying to give us the best shot we have of boss kills and shiny lootz. Given the choice, I'm sure they'd prefer that I'm calling out my status than calling them out. How many times do you have to be mind controlled before you learn to bite, hmm? (Whoops, the Bitch came out after all!)
What do you call out in your raids? Do you help announce timers, remind players to focus an add, or speak out when you are locked down by a raid mechanic? Do you appreciate it when your tanks and healers are proactive in vent, or does that healadin drive you crazy?