The use of egg trays as a sound proofing material has been practiced for as long as I can remember. To this day, it is still fairly common to see small rehearsal and home recording studios with an array of egg crates mounted on their walls. Students in class even talk about being in such studios and claim how helpful they can be.
You only need to know one thing about egg crates: they are for storing eggs and should remain as such.
While they may provide some aesthetic value to certain people, egg crates do not offer any practical benefits as far as sound proofing and acoustic treatment are concerned. Some panels are shaped like egg crates, but they are made of specialized acoustic foam shaped in a purposeful manner.
Below is a video that explains the physics that debunks this myth: