In an electrochemical cell, say a galvanic cell, if 2 electrons leave the anode for the cathode, do you have to always reduce the cathode side with 2 electrons? or can you use 1 electron when you can?

I don't see any problem with reducing 1 electron at the cathode. You'll just use up your cathode material twice as fast as the anode material.

yes, I looked it up, you can use 1 or 2. Actually, 2e's gives the same standard reduction potential as 1 e. Additionaly, using 1 or 2 doesn't matter in nenst equation either; due to the mathematics of the equation. Thanks