Yes the double batch method does bring up the potential for waste, but cures (such as honey, potatoes, etc.) for oversalting alter the flavor profile, which in turns threatens the consistency of product that brings in the guest in the first place. There are always tradeoffs when correcting situations that if done correctly the first time would not be an issue.
Lets say that 5 gallons of soup is made and it is too salty. Because you can't change the salt content you are going to have to make another batch anyway. Another 5 gallons is made without salt and the 2 are combined. So now there are 10 gallons. You sell 8 gallons and waste 2, as opposed to wasting 5 gallons.
I don't like waste. It can be the death of a restaurant. So can inconsistency of product offered to guests. Just right one time, too starchy another time, too sweet a third...wth!!!