I won't go back and edit earlier chapters until the whole book is written.
But say I've written half a chapter — the next day, I'll definitely reread it and make some small fixes. In my experience there usually aren't many. I'm still in that euphoric state of having written it myself. I like the way I write. I catch myself smiling at what's on the page. But any serious editing waits until the manuscript is done. Honestly, I don't even really see the problems until the book is finished.
Sometimes I even get stuck on a paragraph, rewrite it, rewrite it again, and then just give up and move on. I'll change it all during the edit, and by then my eye won't be so worn out from staring at it. You see the clumsy spot — and you walk past it. That takes trusting yourself: I'll come back and fix it. A draft isn't the final text. It doesn't have to be beautiful. It has to be finished.
Still, you have to keep moving toward the goal — toward the end. Eventually I'll have a finished manuscript, and I'll be able to see the whole picture. Every storyline resolved, every character having done everything they were meant to do — and then I can polish it to my heart's content.
Once you have one finished chapter, then two, then the whole book — you'll realize you can edit all of it in far less time than you'd have spent stopping at every single page along the way. Because you'll see the whole thing at once, and you'll edit with real intention — instead of endlessly polishing the opening without knowing how the middle is even going to end.
Fixing an awkward spot in chapter three is five minutes of work. But an awkward spot that gets you stuck, so the book never gets finished — that's a book lost. So don't edit a page you haven't finished writing. Finish it.