Not sure which version of OS X you're using but since 10.4.4 (I think) it has been able to run all the daily/weekly/monthly tasks without any help from the user. It simply keeps track of when they were last run and compares that time to the current time and runs them as needed. It
does use a different mechanism to run them but that's too geeky for me to remember. The point is, there is no need to have special apps or to leave the machine on 24/7 to have this maintenance stuff done anymore. I'm betting you know this, however, and just enjoy seeing it done when
you want it done. I'm somewhat a 'control-freak' myself. Some would say more of the latter, in fact!