Make smoothies with it! (https://www.youtube.com/watch?v=yGRJVvGoS6U)
Clever.
Why not just use the blender jar & lid?
You could. But blender jars are most often big--quart-sized, with a handle. I think this guy's idea was to use a small jar, so he wouldn't have to store a bulky blender jar... and of course using the drill motor avoids the need for a blender base.