"Coach, what other pitching rules would you like me to ignore because you feel they don't offer the pitcher any advantage? Shall I blow off when she steps on the plate with her hands together? What about if she separates them and decides to bring them back together? Oh, and surely when she steps back with her non-pivot foot and it lands outside the 24" lane, there can't possibly be any advantage gained there, right?"
Seriously, it's a pitching rule. God knows too many of us fail to enforce a lot of those violations already.
Now, if you can't tell that the pitcher has a small portion of her pivot foot overlapping the plate because it's slightly covered with dirt, or perhaps the plate is chewed up in front and no longer a straight 24" edge, I can see giving her the benefit of the doubt. But if it is crystal clear that she has no part of that foot on top of the plate, why give her a free pass?