This is simply a back cover for E3-sized mainboards. Fits the Creality V1.1.X boards, V4.2.X boards, TH3D EZBoard, probably some SKR Mini E3 boards.

Has a TH3D logo on it for aesthetics.

Just protection for the back side of the board. Could be used to assist with storage, for testing purposes, you could stick it to the outside of an enclosure, etc.