How to use "unused" keys / indicators on the keyboard

Everyone knows that even on modern keyboards there are keys / indicators that we practically do not use (a bright example is SCROLL LOCK, PAUSE / BREAK).

It is also not entirely clear what users of * nix systems do with the WIN buttons they got. No one uses the context menu key (to the right next to WIN). Separately, the F1-F12 function keys are almost never used (except for a few, such as F1, F3), they are more often used in the CTRL + F combination ... People who do not need to use screenshots do not use PRINT SCREEN.

For example, I recently set myself a change of layouts on the left WIN (OS Kubuntu), instead of the usual LCTRL + LSHIFT - while getting used to it. Also on the current layout informs indicator SCROLL LOCK.

Can anyone have their own recipes for using such keys?