added the comment:
You mean "Table of Contents"? The index at the end serves as a bookmark, right? Also, Table of Contents might add up couple of more pages to traverse.
I don't need subsubsections to be in the table of content. But I think
it is making sense to add them in the bookmarks, as the bookmarks can
be folded even if there are many bookmarks for subsubsections. I'm not
refereeing to index.