Mainly for the hell of it. I like driving fast, and I do plan on tracking the vehicle at some point. Just so you know, it tops at 155 according to manufacturer specs, and I've tested that on an open flat road using a gps to determine my speed and can attest that it actually tops at 153 (but it's close). The OEM tires are rated for 149MPH, so 153 isn't too much higher than the speed rating on the OEM tires, although I did quickly decelerate after determining the top speed so as to reduce the probability of having a tire malfunction. I wouldn't consider anything over 110 a safe speed in any vehicle on the street, and under most conditions anything over 90 isn't really safe. That said, having the speed available and occasionally being able to exercise it does increase the fun of vehicle ownership.
This may actually end up being an exercise in futility, because I'm looking at just buying a high-end sports car within the next year in addition to my Azera, although I'd have to track it only since the insurance premiums on the vehicle I'm looking at are outrageous.