I do about 6 rally balls of volleys and 3-4 overheads.
It's not much, but I like to see if I can place balls deep off of an opponents normal rally pace and spin. Tells me how well I will be able to volley off a good approach.
I'm indifferent on the overheads. I guess weather is a factor, but I just don't like too many overhea swings if it can be avoided.