If a repairman removes the headliner to fix something, what is he fixing?

If a repairman removes the headliner to fix something, what is he fixing?

It depends on the year model, the older cars didn't have much up there. But the newer ones have a lot up there. He could be repairing light wiring, sunroof parts, removing vinyl top molding parts, rear moldings, cell phones, air conditoning ducts, etc. -- and there is probably a lot more things that I can't think of right now.