There's another school of thought that say's when you last ran the motor, you probable shut it down while the oil was hot, so any crud that is in the oil has now drained down and is sitting in the pan ready to be removed. If you fire it and warm the oil, you have now re-distributed any crud in the oil back throughout the motor, and chances are it won't all drain down before you're done draining it. I guess it just depends on how critical getting all the shit out of the pan is to you.