Debugging keyboard shortcuts is the first thing that comes to mind. Esc is also used regularly. I always bind my keyboard to use the fn# keys without pressing

Debugging keyboard shortcuts is the first thing that comes to mind. Esc is also used regularly. I always bind my keyboard to use the fn# keys without pressing "fn", usually in the BIOS, so I only press "fn" for the other special features (brightness, media, etc., that laptop makers map arbitrarily to the fn# keys)