I leave mine on .It is harder on hardware to shutdown and reboot. I leave my machine doing Foldng@home all day. I don't worry about the electric charges that it produces because .I have reduced my carbon/electrical footprint more than what I use with the folding. and plan on reducing it further. Most people don't realize how much power all their appliance and lighting take...just switching your lighting from bulb to LED would probably pay for the power used by your computer. Going green is the way to go...but going green with purpose is better. Folding helps medical science that could one day save a member of your family. A reason enough for me to continue that while finding ways to go green.