Adding a file used to mean opening an upload control, finding the document again, and confirming it. If the file is already on the desktop, that dialog is an extra trip.
You can drag a document onto the dashboard to add it. Drop it on the workspace and it is added. You do not have to open an upload dialog first.
The upload path is still there for anyone who wants it. The drop is the shorter way in when the file is already in hand.
