Isn't it obvious? 2 advantages:What the hell is the point of being a medic when you're in a jet 1000 feet in the air and going 400mph?
1. You can see on the minimap where your team is dying. So, if you see no-one is alive at a flag but there's a bunch of critically injured people, then there's obviously enemies in the area and you ought to bomb the flag (similarly, if you see a cluster of dead guys half way between flags, it probably means they've just been mowed down by armour or a chopper or something).
2. When you fly out of bounds (which inevitably happens, sometimes through choice, other times through making a mistake) you can survive longer and also heal yourself back up if you manage to make it back into the play area.