Simple explanation.

Waiter to manager: They're back for dessert.

Manager to waiter: How nice of them. Comp their dessert, will you?

Waiter to manager: Will do.

Waiter then takes order, and rings in parts of order that aren't
desserts. Because they aren't desserts. Because that's how waitstaff
thinks. If it's not A, it's not A. If we only have Pepsi, don't serve
Pepsi to someone who orders Coke without asking "Is Pepsi okay?" Ditto
"raw or creamy horseradish?" "No decaf, but we have Sanka." Etc.

--Blair
"Cheebourgi cheebourgi cheebourgi cheep cheep cheep!"