Of course I asked Dan that, and although I wasn't completely satisfied with the answer, I learned a long time ago not to question Dan's answers.
Basically he says that it is the easiest way to get the scooter out of your hands and out of your way, while still keeping control over it. To get the scooter back you just reach down and grab the shroud and you're ready to go again. The key being that it's supposed to make life easier for the diver. I found it made things a lot tougher (especially in current), but Dan swears it will become easy with time (sorta like a valve drill). I'll give it a go for a while and see...
Not sure I believe Dan on this one but like you I'll also give it a go.