Normally, synced files are fully downloaded to your computer and they take up hard drive space. With Smart Sync, you can make files and folders online-only. Online-only files use just a small amount of hard drive space to store information like the file name, size, and thumbnail, but the full contents of the files are stored securely in the Dropbox cloud. You’ll always see your online-only files on your computer, so when you need them, you can open them with just a click.