Where a cash and carry trade is cumbersome it becomes easily manipulated and only large commercials can execute a cash and carry. This is extremely common in energy contracts where a cash lot may, very well be a tanker. One of the reasons why crude went negative was the inability to trade the spot. Without a method to hedge the spot, wild data can result. If you can actually trade spot - there are times you pretty much can coin money.
It's also why most of the big commercials still operate in house trading desks.