I agree with roger using dull tools does not cause catches, catches are caused solely by tools not being presented to the work correctly. It is important to prevent tear out and make cleaner cuts but knowing what causes catches is important for safety. That claim is simply false while I don't have rogers experience I do have a fair amount of experience on a lathe. Sharpness does however have an effect on the quality of the cut and long term means less time sanding and prep for finish. I really think its important to make that distinction because new turners often get fustrated not knowing why the tool jumps on the tool rest. telling them to sharpen more often isnt going to stop that.