[warnerwh]

After running two lines into my living room I've learned that neutral and ground are tied together at the breaker box.  This makes me wonder what a separate wire for ground is for.  TIA

[Dan Banquer]

The separate ground is put there to be separate direct path back to earth ground. Think of  it as a safety ground or as an added shield ground, or both. In any case, the great bulk of surge suppressors, and RFI/EMI filters all "dump" to that third prong.  This is to differentiate it from Neutral which is supposed to have all of the main current returning to earth.
   Hope this helps.
                 d.b.