I love the feeling of being able to go back through a manuscript and send so much stuff to the virtual Goodwill of the writing world.
I've just started another revision of the second book in my series. It's been probably three months since I finished the last revision. Enter the Goodwill run. First three chapters? Gone (with the very minor exception of a couple key sentences).
It's so hard to realize what is backstory when I first start writing something. So much of it seems so necessary at the time. Even months later on a fifth rewrite, it's hard. Maybe because I get so close to what I write, and even a couple weeks between rewrites isn't enough. But now it's crystal clear.
(OK, in all fairness, a little pointer from a qualified editor certainly helps in pointing me in the right direction).