That's one use case, but you can use them to execute any elisp code. So when I encounter a new major mode I plan to use, while going through its docs I make hyd

That's one use case, but you can use them to execute any elisp code. So when I encounter a new major mode I plan to use, while going through its docs I make hydras for keystrokes/commands I plan to use. This way I don't need to look up my notes, nor do I need to memorize keystrokes.