A small example.

I thought I'd provide a small example of the benefits of rewriting.

In the original draft, I have Alex, the young techgeek member of the crew, deciphering the Necronomicon and finding the formulas to close the Portals from Cthulhu.  He is asked to copy the formulas, but copy machines don't work in the Great Library, so he goes off with Gorgon nympths to handcopy the spells.

Then in the battle, he's clutching a handful of papers and trying to read them with fire and brimstone going on all around him.

So -- in later drafts, I consolidate the library chapter with an earlier chapter.  Instead, Cobb calls Alex on the phone and tells him, since he can't copy the Necronomicon, he'll have to memorize it.

Problem is, I lose that nice bit of visual business of him clutching loose papers while trying to recite the spell in the heat of battle.

For the final rewrite, I still keep the consolidated chapter and the cellphone, (which are a streamlining improvement) but I have Cobb telling him that he needs to "write it down."  That way I can keep the flying papers scene.  But it also dovetails nicely with another key plot point.  Up until the events in the book, Cobb has been banished from the Great Library by the love of his life, Lillian, for having destroyed a book -- which he thought was the Necronomicon.

So Alex shows up for battle with a bunch of mismatched pages of paper and tells Cobb that it was lucky he had a pencil stub in his pocket, because the Gorgons don't use paper to keep track of books (also a nice point, because I've established that the Gorgons use their 'tendrils', which look like snakes, to organize the books).

So Cobb asks him where he got the paper, and Alex tells him that Lillian let him tear out blank pages from various books, Cobb is astonished.  Because we've already seen how protective Lillian is of her books.  Then in the battle scenes, the papers being hard to hold and flying away make even more sense.

OK.  A really tiny example, and somewhat subtle -- but all the little pieces fit.

So what I hope to do is improve the book in a hundred small but fitting ways.  If I do that,  I've without a doubt made it a better book.

Constant rewriting tends to firm up the backstory, and clarify the motivations, and give me more chances to explain what's going on.