I was privileged to be on the editing team for this. It was a joy to work on and can assure you a highly entertaining read.
Proofreading is more than a manual spell-check. This is the last stage of editing prior to publication. It's vital not to leave this stage to chance. It allows you to look for colour variations, layout issues, spacing, typeface consistency, missing items, tense and tone errors, content errors, inconsistent capitalisation, that page numbers are correct, and other formatting problems.