Your question is a good one. I use auto sync but it IS a battery killer. Some things were better in 1.5.

 

I believe that autosync is a push from gmail, so it is not a battery killer, and it is also why you won't find a refresh period, since you never check the server, it pushes when you get something. The only way it is a battery killer is if you get emails very frequently, and that will be a killer doing it manually as well.

This is based on my understanding of the way the gmail app was in 1.5. So in some ways 2.1 is the same as 1.5.