Slipstream - I remember the 1960's where F1's at fast tracks such as Monza, would often form groups of cars which stayed together. The slipstream helped enough, to make a slower car fast enough for more excitement. A small effect was enough. A bigger effect came from GT cars, as they had a bigger frontal area, which moved more air sideways. The Mulsanne at Le mans was famous for this.
A large jet plane moves enough air, they wait 2 minutes between each takeoff, to avoid dangerous turbulence. Size and speed. Wind tunnel testing in the 1970's, showed how slipstream and drag could be reduced. Much less now than then.