Typically a keyboard hook is related to a hotkey in the program. Ie "press ctrl+space to do this and that", that'll require a keyboard hook. Some applications require it for general text input, for example PartyPoker hooks the keyboard to use with the chat box (however typing bets works fine when blocked).

You'll also see programs taking screenshots when you access drop-down menus alot, I have no idea why they do it though. I typically just deny everything, then if there's a problem with using the program I'll manually allow it (if I've decided to trust the program).