This is a simple wedge to prevent the drawer face (or drawer slide) from catching on the cabinet door when closing.
I had one particular set of drawers inside a cabinet against a wall, and the cabinet door didn't always open far enough, causing the drawer face or slide to catch on the face of the door (causing it to stop abruptly or scratch the inside of the door).
This simple wedge screws on slightly in front of the drawer slide front lip and pushes the door out of the way when closing.