[Bicycle Bob]

People can put out more power for shorter periods. They are a bit like electric motors with a severe overheating problem that way. Having riders in a pace line rotate to the front averages the overall effort, and puts the best-rested rider at the front to push the air.

P & G works because even though you loose efficiency with the higher peak drag for a given average, you gain even more by not making the engine suck on a tiny hole to get air for just a bit of power. With less restriction, it runs more efficiently, and stores energy as kinetic energy in the whole car for use during the glide.