I usually revise after I finish a chapter, and that's the polishing kind of revising. I'm a bit of a perfectionist, which sucks ass in this profession, but anyway....
Even after I revise it/polish it, after a good handful of chapters (no real set count) I'll go back through them and polish/revise again. When I got to the smack middle of my WIP I took a good several months break from block or fatigue or whatever it was I had. I started up again, leaving my first chapter alone. I'm still at odds with knowing if it is where it should be or not, but now that I've reached the half way point I want to finish it.
When I start to write for the day, if it's in a chapter, I'll start at the beginning of the chapter I'm writing in to get my fluidity going, but also tend to edit if I see anything. I'm still a poor editor though and hope to gain better skills as I keep doing this.
In the long run I guess, I edit/revise/polish as I go so that when I'm finished I'm finished and there isn't too much more for me to do so my eagerness can be rewarded by sending it to my beta readers. All that I will have left are first and last chapter tightening, and little tidbits I make notes to add to other chapters to tie everything together.