Long travel a arms use a longer shock, this allows the shock tuner to have more flexibility and options for valving the shock for different areas of piston travel.
A standard travel set of a arms uses a stock length shock.  Not as much tunability as a long travel.
A long travel a arm does NOT mean that you will necessarily get more wheel travel.
A standard travel shock might have around a 4 inch stroke, a lt shock might have a 5 1/2 inch stroke, for example.  The geometry of the a arms, leverage ratio, and ball joints/ heim ends it what determines the wheel travel.