As the second line of defence against acoustic problems, absorption is applied in a tactical way, very much like diffusion and bass trap treatment. Absorption is generally applied to the “live-end” of the room (where the monitors are located).
To determine where absorption should be applied, the mix position is ultimately what dictates these decisions. The idea is to have no reflective potential off the left and right sides of a room as well as the ceiling.
Although, material professionally designed for absorption is the most ideal, objects such as furniture, photo frames, desks and chairs, will all assist in absorption and diffusion. Not to mention people! A carpeted floor and soft material walls are a commonality among most professional studios, for the very reason of absorption.
As you reach the “dead-end” of the room (the back of the control room), absorption is no longer the most effective method of acoustic treatment, however, it absolutely does not hurt.
That being said, if you kill absolutely all reflections with absorption, the room becomes unnatural and loses is character. Theres a reason why engineers, producers and artists favour production in particular control rooms and studio floors.