There is a clear advantage to the diagonal cut sandwich.
The Vineyard owner in the readings today gave equal portions to all men that labored for him. The diagonal cut takes the guessing game away from the dilemma of perfectly squared equal portions. Though the two parts look different, it doesn't really matter how big the two sides are if you are eating the whole thing yourself. God is bountiful in his mercy and divvies it up like a diagonal cut. We all get the whole she-bang.