The only reason I can see running it with the cover off is to allow more airflow, and I guess to cool it. I never ran mine off, I would see racers do it. Its loud enough with it on, didn't need to add to the noise especially when I added the dry clutch.... NOISY! lol
That was pretty common as I recall back when I had a Rhino. I had that same setup but left my lid on. I think there were actually tests done back in the day that proved the lid actually helped performance some how on a stock engine and removing it hurt performance. Perhaps Chris from Benchmark can chime in.
i have been running it off since i got it, but last night i was just buttoning things back up, and I was just curious as to if others were running it like that...
I've been playing with the CVT this winter on my Rhino and have left the cover off while trying different weights and springs, while trying to tune the CVT. Haven't really noticed any difference while doing trial rides with it off verse it on. But my motor is pretty much stock. Whatever it's worth.