It's true. We could go over it time and again and still find things to improve. Yet, once the book is published, the reader will be exposed to any shortfalls. Before my novel Still Rock Water is published at the end of this month, I asked my contact at Solstice Publishing if I had time to go over it one more time. He hadn't yet handed it over to an editor, so he told me to go ahead. He said, "A book is never finished, only abandoned."
I interpret this as the author deserts/gives up on each book for sale. And yet, there must be a time to let go and release the story to the public. A writer could continue editing until they are old and grey and still not be satisfied.
I'm glad I have the opportunity to correct any glitches I find as I read out loud. The time-constraint is daunting. What if I don't reach the end before the publisher requests the work? What if I miss some major boo-boo? Will the editor find what I've missed? Depends on the quality of the person assigned.