Editing is a painstaking and tedious, but necessary process. A lot of concentration goes into it, because what you are changing and writing is ultimately going to be the finished product that the reader takes in. So everything has to make sense, all the plot points need to connect, words have to sound right and be spelled right.
My history with suggested edits sent back to me has tended to be comprised of the overuse of certain words, and word arrangement changes and in some cases, total deletions. On the odd occasion I've received awesome praise for a twist in the storyline.
All in all it has taught me more as I do my own form of rewriting and editing before submitting my work. I find myself correcting myself and remembering a former editor's suggestion as I work.