It is installed for improved efficiency, in addition to the baby "mud flaps" in front of the rear wheels. They are also called "spats." You shouldn't miss much by removing it.
By spats you mean the mini little "mud flap" in FRONT of the rear wheels, right? If so, I have a new '13 SR5 and DO NOT have the spats. I DO have mini little mud flaps BEHIND the front wheels. Easily removable and those will probably be taken off soon on my ride.