[ Tables of contents ]

If a book has a table of contents (ToC), then it probably contains technical information.  Or, at least, it probably isn’t fiction (though some novels have them). 

Tables of contents help orient the reader to what the document contains.  It’s like a meeting agenda: it sets the scene for what to expect from that book (or meeting). 

A document longer than 5 pages should probably have a ToC.  For documents over 10 pages, I’d argue there certainly should be one.

The ToC shows the structure and organisation of the document. Without a ToC, a reader can’t get the big picture.