Doing revision of a book is OK. but the issue is, when we start writing a book, the version may be say 0.2, and when we release the book, the version may be 0.4. So the main thing is, the book got outdated in the release itself. So just think about our situation. Do we have motivation to write another book? I had this situation and I have changed the content of the book at the end of final edit. This is painful.