Sometimes there are other files of interest added to the FTP site, e.g., Plugin SDK, and it is faster (i.e., less effort on my part) to just use TCC to download "everything newer than last download" than to update everything manually. When files whose content has not changed have a newer timestamp, conforming to the Unix developers' misbegotten idea that making a copy of a book is a new book, I end up with wasted downloads.