Yes there is a big difference... your hard-drive is not on your machine, its in the cloud. It will be hard for people to understand at first.
Think of your gmail account (if you have one) ... before you used to have to download all that mail onto your laptop, use up harddrive space, and then view your email in Outlook or Eudora. Now... with gmail, you just login, and its all there. Its in the cloud, but it feels like its right on your computer.
Then think of Chromebooks and the cloud. All your docs and files don't need to be on your computer. They will be accessible anytime, online or offline, via Google's cloud.