what's the good of (doing something)
What reason is there (to do something); why should one bother (doing something)? What's the good of trying? I just don't have the brains for this class. What's the good of making your bed each morning when you're just going to mess up the sheets again at night?
what's the good of
Also, what's the use of. What purpose or advantage is there in, as in What's the good of crying when you can't do anything about it? or What's the use of getting a doctorate in philosophy when you won't be able to get a job afterward? This idiom was first recorded in 1701.