Milo: Welcome to AcesHigh. Some damage to a field is persistant, i.e. can still remain in effect after capture. Fuel, ammo and troop barracks, for example. That's why you don't necessarily want to bomb the snot out of a field before capture, especially if your planning on using it immediately to launch an assault on the next field in line. You don't even need to bomb the ack to capture it...theoretically. The Buccaneers actually made a mass drop on a field once using 10 or 11 transports, and managed to capture it intact. That was a while ago though, and it was a two-ack field. Ack accuracy changes may have made this unworkable now; haven't tried it lately. Hope that helps.
Sabre (a.k.a. Rojo)