Normally placed upon boats that the hull isn't specifically designed for a jet pump and used to enhance smooth water flow to the pump... Alot of boats that do not have the flat section at the back and shops will put them on to increase that ability to capture enough water effectively... Same thing for extended plates from transom to the pump. Again normally a hull design problem and an attempt to gather better water at the pump. Not needed at all for the right hull...
Agree 100% if your going to run skinny water- they won't last long.