Correcting:
1) poorly formatted chapter heading/titles
2) fixing broken (up) paragraphs)
3) removing stray bits (ads, page numbers...)
4) Making the overall style 'Your Way' or to be conversion friendly
5) Fixing Spelling errors

6) Fixing gross HTML usage perversions

7) Making a quick TOC
"
If you like your book 'as delivered', don't bother. "There is nothing here for you..Move along."