Should the table of contents of a thesis include beyond heading level 3? Should the table of contents of a thesis include beyond heading level 3?

I would like to know if there is a rule specifying this issue either in MLA or APA?
In general, tables of content shouldn't span more than two pages, otherwise they lose their utility of being a quick guide to the structure of the content.

A good keyword index at the rear of the document can handle many of the issues in their stead. That is, if you want people to be able to quickly see where you described the laser engraving process, then "laser engraving" can have a keyword in the index. Or if you make an argument against Talcott Parson's sick role, similarly you can note both "Talcott Parsons" and "sick role" at the back.

(note: I do encourage my grad students to CREATE extremely detailed tables of contents that lay out their entire argument. This helps them write their dissertations as it gives a roadmap and structure. But when it comes time to submit their thesis to the university, or revise for publication, they should strip their table of contents back down to a minimum of one or two levels).