As for shutting down machines vs. leaving them on, I did a study once on our old HP servers here years ago and close to 80% of our hard drive failures came during reboots. Those things would run forever, but each time we rebooted them and those hard drives would spin down and back up, we would hold our breath. Like everything else, technology has advanced over the past decade, and I can’t remember the last time I had an internal hard drive just up and die with no warning. In fact, the last two hard drives I had fail were both USB drives without external power adapters. I assume they either died from getting banged around, or from not getting enough power.