I don't have any issues with my 622, so I left my download at the default and I am not going to get up to check what it does. If you need to know, just change the time of the download and watch and see what it does.
From what I've seen it only updates the guide nightly (3:00am default) and it will only reboot when it downloads new software. I always turn my receivers off at night, perform an additional soft reboot when I know they received new software, and do a soft reboot the last weekend of every month just for SnG. I have been doing the monthly reboot since we got VOOM DBS service a couple years ago. I do it when I add Rid-X to our septic system and it has proven to keep the system running clean (both VOOM and Dish Network service); we don't see 99% of crap others report with their receivers.