I imagine long range healing using deployable turet. Or maybe heal deployable player (aka the guy manning the turret)?
You can't heal people manning the MANA turrets with the heal gun. I think you can still heal them with the F button heal ability, though. I think it's a valid point that you should be able to.
I would assume the deployable healing ability was the medic themselves, but a healing deployable would be fantastic not to mention a bit op especially if multiple shield/healing deployables were stuck in place and it forces people to constantly camp door way and such.