As Ken alluded to the major track advantage of 2 piece brake assembly (separate rotor bolted to a hat or hub) is less heat transfer to the wheel hub.Faster cool down of the rotor.This also prolongs wheel bearing life.
Actually, I think the major track advantage is the flexible connection between the outer "ring" and the inner "hat". That way, when the ring heats up from track use, it can expand out away from the hat, with a minimum of internal stress. Whereas with a one-piece rotor, it's all one piece, so when the outer part gets hotter than the inner part, it wants to expand more, and there's a lot of resulting stress, which is what causes cracks to develop relatively quickly.
And there's also the convenience of not having to change rotors or miss track time in the middle of an event due to cracked rotors, or at least, not having to do so as often. My rotor lifespan varied, but on average the two-piece rotors lasted twice as many track miles as the one-piece.
Theoretically, another advantage of two-piece rotors is that you can replace the rings while re-using the hats, thereby saving money. However, in my experience, the rings and the connecting hardware (plus somebody's labor to R&R them) cost almost as much to replace as replacing the entire assembly, so the savings aren't real.
Of course, the downside is that the two-piece rotors cost a whole lot more than one-piece ones.
I know what NA1 and NA2 are, but because the year matches the brake change and many refer to it that way, I did too. Not a big deal except a technicality. Also, his signature also says '91 NSX which was a previous ride. That is what I saw on a quick glance. But what I said remains a fact. Racing brake (nor anyone else) does not have a drop-in 2 piece rotor. I think he already stated he wanted it for bling, otherwise I would talk him out of the racing brake to begin with for track use.
