First of all, welcome to the forum!
Well, I guess it would try to fetch your email and stuff with the WiFi off, but of course it won't work. The other option is to set yours up so that it fetches manually. (That's what I do)
I just leave my WiFi on all the time, even when I am not at home. I know it is constantly looking for a WiFi connection, so I suppose you might be saving a little battery life by shutting it off, but the battery life is so phenomenal on the iPad (as opposed to the iPod Touch or iPhone) that I don't even worry about it. At the most, you might extend the battery life by a few minutes.
