Probably because I have never even gotten one. I know they do something with attacking cities but I generally already have rams or go for catapults.You forgot Siege Tower (Not sure what that does, but it does say something about "automatic damage" in the civilopedia entry).
The Medic and Balloon are so freaking good. I suggest you consider promoted units pairing with supports.You can also park 2 mech infs with 2 medics in front of an AI city and fortify them and go afk. It's ridiculous.
You can also build 7 observation ballons and have one artillery with +7 range and six with with +4.
Yes, that is the point of sending a Medic with them. They are going to eat some bombardments from cities along the way. The Medic mitigates this so they don't have to spend as many moves on tearing up farms for healing.Light cavs with medic? Sounds great. Do they heal after pillaging/moving?