That entirely depends on usage.  I use mine a few times a week or so, so I shut it down.  That also clears the RAM.  If 8 hrs/day, I'd still shut it down in between uses.  Have programs/apps, a work environment, that needs it on 24/7, then definitely leave it on with an occasional restart to clear RAM. Sleep is also an option to save energy in between uses, like short breaks.
Do you recommend leaving your computer running all the time or shutting it down? Why or why not? For more questions regarding this contest, please visit the Information Page here.
DS 07/24: Do you recommend leaving your computer running all the time or 
shutting it down?