An absorption panel, as its name suggests, is meant to absorb. It dissipates the acoustic energy inside it and only reflects a small amount.
The diffusion panels fragment and diffuse that energy by scattering it.
In order to reduce and control reverberation in rooms, we use absorbers or a combination of absorber/diffuser, since diffusers also fragment the sound in a controlled way.
In other cases, when a reverberation increase is intended, diffusers are then used to increase the reverberation time.