At the beginning
1. shows people a ToC is available. A lot won't know they can reach it as ToCs are badly managed on their device (say three taps away in an obscure menu, which is just some terrible and annoying UI/UX). In some cases (non-fiction), when we know the ToC is a "navigational pivot" since it is a guide and people will use it in a non-linear manner, we even add an extra layer of navigational network (breadcrumbs at the beginning of each part) so that the ToC is available anywhere anytime… and people send mails to thank us because their device's User Interface is just plain bad.
2. some descriptions are so vague that you download a sample to judge the value of the book. If you put the ToC at the beginning of the book, it (sort of) helps undecided people purchase the book as they can get extra information, especially with non-fiction.
Last edited by BangBangO; 08-10-2012 at 05:22 AM.