Ritsu-sensei's students tend to have something they can do really well, apart from fighting. Actually, it's not generally one thing. I'm guessing Soubi can also cook and treat injuries and stuff. But there's one thing that has no obvious, practical application. You'd have to ask him what it's for. [It's pretty clear from the emphasis he puts on the word that he means Ritsu, not Soubi.] It's classic, though. Not optional. Fighters that are being trained as objects don't get free time. And much less art supplies.