Mine throws everyday, the days he doesn't pitch or do pen he tosses, not on the mound, it is not required. What does change daily is his conditioning routine.
Bum makes a great suggestion for HS, pitcher can get his BP in an inning in a game as a reliever on third day, if he has not thrown too much his last outing. It helps arms. I've seen this in the college game, on pitchers BP day he may pitch an inning depending on his last outing or if needed, if not he pitches his BP. When son was in college, he would start a weekday, max innings for a win then do his pen as reliever on the weekend. As a weekend guy expected to go 7 at least, it wasn't done.
A coach can get so much out of their pitching staff if they use them and treat them wisely.