Jim Hamm keeps finding helpful stuff, "Here is a helpful website with information for routine maintenance on your Mac. It has been recently updated.
"If you leave your Mac shutdown at night, then the routine 'maintenance scripts' from Apple won't run -- but they will if you leave your Mac in a sleep mode. Normally, even if these scripts are not run you probably won't experience a problem with your Mac. I don't leave my Mac on at night, so the scripts have never run on my MacBook Air and I'm not experiencing any problems. Having said that, though, it is probably a good idea to have these run occasionally."