i usually leave it on 24/7 - however the more programs i open and close, it starts to jitter and act slow - so an occasional restart brings it back to new
I think the main reason for argument that it's good is the hard drive lasts longer without starting and stopping all the time
however this was information I heard 15 years ago
I'm sure modern HD's respond better
I leave mine on, because I work at home, I sleep for a few hours then back at the computer for many hours - i'm really busy these days!
-yes, monitor off
intel mac pro 2.66 LOGIC 8