Benefits? Most certainly and not just for identifying mechanical errors. Imagine reading the same book for the fifteenth or twentieth time? Reckon you would glaze over? Uh huh, that is what happens and it is important to note where. Those saggy spots are the boring bits and glazing is identifying that they need to come out.
Still hate an obnoxious character? Now that is good as the feelings are working. This was not a lovely person to start with.
Basically, this is the time to sheer off all the fluff to leave a story slick and shiny. 20,000k tomes will not cut the ice if half that wordage is worthless fluff. The real story needs to emerge clean and fresh.