I've heard a few different point of views one this. I've heard its better to shut down because you won't be using energy then and not as much stress on component. I have also heard its better to sleep because of the energy required for boot and when you shut down and start up, the heating and cooling of the components make the contract and expand which will put stress on them. Power isn't one of my major concern, my major concern is which will make a Mac Pro last longer. With an SSD as the boot drive, it won't need as much power as a mechanical drive so I don't need to worry about that. Does anyone know which is better? Also, which do you prefer?