The most cut and dry basic grass roots amateur racer fact about ground effect is simply the fact that when wings, splitters and diffusers get close to a fixed object (the ground) they become more efficient. Any amount of ground effect for amateurs, grassroots drivers and mechanics is a good thing. Just remember to keep your splitters and diffusers close to the ground for better performance.
Diffusers do what the title says, “diffuse turbulent air”. Diffusers, for the most part are installed at the rear of the car as close to the ground as possible and they aide in down force by taking advantage of “ground effect”.