When you ride a properly tightened crank, as you apply pressure to the pedal, you leverage the crank slightly further onto the spindle, away from the bolt head.
I would like to know where this information is documented. In all my years as an industrial mechanic, I never once saw a tapered fit push up the taper, during use. Down, yes, but not up. Please understand, I am not arguing, just asking where I can learn more about this.