Besides the obvious that coil-o can adjust your ride height. Let's say you adjust a coil-o to the same ride height of any aftermarket springs and both having the same spring rate, what are the advantage with coil-o in this particular situation? Does coil-o typically handle better over conventional performance springs?

 

The GC setup uses the Eibach race springs, which are shorter, linear rate, and lighter. The lighter weight decrease unsprung weight which also improves handling and acceleration.
Pic of GC next to Pro Kit springs for a Z32

For most people, they get coilovers to slam the car. For racers, the coilovers allow for the car to be corner balanced for better weight distribution or to setup the vehicle for the driver's driving style. On my Miata (autoXed every other weekend), my rear is about 1" lower than the front so that the rear end stays planted coming out of the turns (oversteer).