The wireless allows you to fire the Sb-600 or SB-800 or groups of these flashed with full metering capabilities through a series of preflashes. You could also use the wireless setting to setoff a low powered flash to trigger studio strobes with their optical slave sensors. Also, think portable studio--2 SB-800's, stands and umbrellas/softboxes for use outdoors.
DPReview has a lot of people using 3 SB-800's for their main light, their fill light, and their background light. You lose this capability with the D50. It is really fun just to play with, too.