I do a lot of editing as I go along too, going back and tweaking stuff I've already written for a chapter or a short when I sit down to write. Sometimes that can really be a good thing because it gets me into the grove of what I was just doing and things just flow, and sometimes it's terrible for me because I have a horrible time turning off the internal editor so I can just move forward and get that first draft out.

I have been known to pick at one paragraph of a short story/chapter for days - which is something I try very hard not to do. But it's difficult for me to move forward when I know there's a problem that's going to have a domino effect throughout the rest of what I'm writing. Plus, it's like a puzzle that I can't stop messing with until I figure it out and sometimes I wish I could just turn that off.