what's the use?

what's the use (of doing something)

What reason is there (to do something); why should I bother (doing something)? A: "OK, so you didn't do so well on the test. Just study a bit harder next time!" B: "What's the use? I'm just not any good at math." What's the use of making your bed each morning when you're just going to mess up the sheets again at night?
See also: use

what’s the ˈuse (of doing something)?

(also what ˈuse is there (in doing something)?) used for emphasizing that you think an action, etc. will not achieve anything: What’s the use of worrying about the weather? You can’t do anything about it.‘Why don’t you try talking to her?’ ‘What’s the use? She’s already made up her mind.’