It might be used as a GND (ground) point/connector/thing (hard to describe) (if you look inside a pc then the shell is metal, the screws are metal, and the things around the screw holes on the motherboard are metal. These all conduct with each other, so if there is a short or a bit of electricity going through the shell then it grounds it rather than shocking your or frying your PC) That sort of thing i think, just connecting ground points. I think it is safe th take it off but what for????