Because OSX is a unix based operating system, it is designed to be running all the time.
In fact, if you turn your OSX based machine off, it is likey to not be able to run at least 3 system level functions that ensure itv funtions correctly. These include (among other things), the rotating of various log files, backing up the Netinfo database, and doing the login accounting (computing how long users have been using the system for). These function are all summarised by three sets of scripts: The Daily, Weekly & Monthlly scripts.
If you INSIST on turning your machine off (lthough DEEP sleep uses virtually no power - all it is doing is keeping the RAM powered), you should get hold of a freeware/shareware app called Mac Janitor, which provideds a user interface to run these 3 scripts manually.