What happens when you give away a book for free that you are also selling?

For American Gods:

68,000 unique visitors to the book pages of American Gods

3,000,000 book pages viewed in aggregate

And that the weekly book sales of American Gods have apparently gone up by 300%, rather than tumbling into the abyss (Neil Gaiman)

So, promoting your book actually works? Wow, who could have seen that coming?

My bigger question is whether it would be a good thing to give away a book chapter by chapter as it is being, let's say, rewritten. Should a book like that be given away chapter by chapter, part by part, or should it be held back until the rewrite is finished?

I am glad Neil put up real numbers. I have heard claims of success but not actual sales figures before. This sounds like a success to me.