Back to my mac question

Hi, I have a question about the .mac feature 'back to my mac'

I asumed this...but I can't find anywhere on the mac sit that confirms it. Does your home mac need to be turned on? Or can you have it off, and when you log onto .mac and log in you can boot the computer up remotly? Because I wouldn't want to leave the house with my mac running all day using power, but It would be very handy to be able to log in, get the files, then shut the computer off again.

Thanks for helping