Camshaft clearance

IF that pump drag forces the cam rearward any time the engine is turning, then why would it be necessary or, even desirable to jerry-rig a cam button; it would never be used... would it? I am thinking, "if it ain't broke, don't fix it." What am I missing? And, to the OP, if you think your English is bad (it isn't!) you should hear our Swedish....