The specific purpose for which they were used inside the door panel, I don't know, however, I've seen this style of clip. That is an intact clip, but there is a mating part with teeth pointed in the opposite direction. The upper smooth piece lifts slightly so that the other half can slide inside. They disassemble without breaking by pushing the upper smooth open. Generally, they are used in applications where that "element" being held might be of varying diameters/shapes. Do you have any wire harnesses inside your door?