Among other alts in The Old Republic, I'm leveling a healer Commando. My original plan was to run instances with this character, but I got bored of waiting in the fleet and went back to questing.
Leveling as a healer in SWTOR is interesting. I generally run with a DPS companion (Aric Jorgan at the moment). For normal pulls, I generally use the regular DPS abilities of the base class. But for strong and elite enemies, I do actually act as a healer. I let Aric kill the mob, and I keep him healed, with the occasional zero-dps attack if incoming damage is light enough.
I actually like it. Normally leveling as a healer means that you level as a very weak DPS and don't use your heals regularly. You only use them if you get into groups.
But healing a companion is very much like healing a regular player, and you get to practice your regular healing rotation.
It's probably slower than leveling as DPS, but it is nice to play solo as a healer, and still act like a healer. I do think that companions make life a lot easier for tanks and healers, allowing them to level with their preferred playstyle and get lots of practice with the correct abilities. It's a lot better than learning how to tank or heal on the fly in an instance.