I use them in Emacs occasionally. It's handy for stuff with ambiguous names. Makefiles (which dialect?), whatever.pl (Perl? Prolog?), whatever.asm/whatever.s (which architecture? Which assembler?), etc.

Also comes in handy for working with files that have an incorrect extension, for whatever reason, or different formatting from all the other files of that type that you work with. (Per-project formatting stuff can often by solved with .dir-locals.el, but not always.)