I do this. Well, mostly.
What really happens when I sit down to write is this:
- Computer on
- Scroll down to spot in WIP (work in progress) where I first started writing yesterday.
- Go over what I wrote yesterday, editing slightly as I go.
- Come to the blank part of the page and pick up where I left off.
So I'm doing minor rewrites every time I sit down to write.
Confession: sometimes I do major rewrites. Like this weekend. I had, well, not an epiphany exactly, but a sort of "aha!" about a minor thread/theme/thingie in my novel. I could see how much better things would work if I incorporated it, but that would involve going back to earlier scenes and changing them to fit my aha! moment.
No, I didn't make a note of the aha! and keep moving forward, as some would suggest. I fricking went back to those earlier scenes and made the necessary changes to fit the aha! I made all the changes in about an hour, so it didn't hold me up hugely, and it relieved my mind to know that the aha! was now where it should be. Then I finished the chapter.
I think the key to rewriting while you're still finishing your first draft is moderation. If you spend more than 20 percent (yes, I picked that number out of the air) of your time rewriting your first draft then this may not be for you. You might need to be one of those forward motion maniacs who allows nothing and no one to get in the way of their first draft. You folks tend to be the all-or-nothing types, the ones with a switch that's off or on, but never in between.
Me, I'm betweeny. I'm good at moderation. I'm almost too good at it. My patience is, yes, almost too well developed. How? Well, mostly in my personal life, so I won't go into it here. But it is possible to be too tolerant, to allow too much time or give too much leeway to things/people/yourself. Every now and then, kicking your own butt, telling someone to leap off a cliff, or yelling at your landlady for not fixing the @#$ing stove after it's been on the fritz for a year is a good thing.
So if you can handle moderation, then a bit of rewriting as you go can work for you. If I'd waited, even with notes I might not have quite grokked the rewrite the way I did yesterday.
Side daydreamy thought: how different would my book be if I'd written it at slightly different times on different days over the past year? How much does nature the day's work depend on the time/place/mood in which its written?