If you can sustain this for twenty minutes, you are now immune to writer's block. You know you can always write. This shifts the question to what to write. You find you can sculpt these chains of drivel. Eventually you start to generate real ideas again.
Even if you never use the things you write in this way, it can be hugely freeing to the mind as you set aside the other things that were distracting you by putting them onto the page and are then clear to focus again on the problem at hand.
This comes from the Artist's Way, which advocates doing this daily as the primary activity of the book / workshop.