Planning to install diffusers but what's the point?

I see lots of people put diffuser panels on the walls, and covering a relatively small Area of their total Wall Square footage.  And I'm thinking what difference does it possibly make unless you paper over a substantial portion of a wall with a diffuser.

A diffuser scatters the pressure amplitude waves, sort of like a wave hitting the edge of a pool and spreading along the side of a pool.  So with all the waves circulating through out a room how could a couple square yds of diffuser panels make a difference. Cosmetically it looks nice I guess.

If you're treating a room and you have a pro do it with diffusers, they do entire walls of the stuff and I guess there may be some justification here.