I kept Hugo's (11) tummy shorter last summer. I think it helped some. This spring, I'm leaving it long, because he (and Piper) are my assistants in several Humane Ed classes for grade school kids. At the end of each session, he does his "play dead" trick and is supposed to end up on his back with all four feet in the air. Sometimes this happens and other times he's ends up on one side.
After some careful consideration, I decided that it would probably be more appropriate for a well endowed male to have some camouflage in his nether regions when sprawling belly up before a crowd of youngsters. And I'd rather not put the teachers or parents in an awkward position, or worse, have them faint. I have no doubt that the topic could come up on the bus ride back to school. So, I'm pretending that it is necessary to keep his tummy as hairy as possible (although having him wear trousers might be amusing).