I haven't used this yet, but I do remember it as a really cool feature of my previous macbook.
But dragging a file doesn't seem to be so easy anymore; half the time, it wants to rename the file instead. No idea why. I also thought it used to be possible to drag a pdf or other document that I have open in an app, to an email and attach it that way. That doesn't seem to work anymore.
For example, dragging the Documents folder into a terminal pane becomes: