I don't use a bug net at all for general blue ridge mountain camping. I think if i was in Florida or Minnesota, I would, but i've never been bothered. Spiders are a worry, but they have never gotten on me as far as I know. The bug net was going to be the last part of my system when I was putting it together, but now I wouldn't bother.
I do think, though, that bug nets add a few degrees of warmth.