While dismantling my extruder for a small mod I accidentally discovered that the worm pulley has so much grip that it will still extrude PLA with the pressure roller removed. It is hard to see on this low quality video but it was extruding 0.4mm filament at 32mm/s.
I will still run it with a roller because it helps to guide it into the tube when self feeding to start a new filament. I also expect softer plastics would need it.
BTW, I have stopped using Vimeo and gone back to YouTube because they added an artificial processing delay unless you pay.