This was certainly not a "need," but more of a curiosity. My other Glocks are all Gen 4s and work fine, assuming the recoil spring has less than 5K on it. What the Gen 6 adds is an OEM mounting system (no more MOS), which means no milling (something my other ones required). The grip angle doesn't bother me since I'm shooting Glocks 99% of the time, but it's certainly different when/if you're switching manufacturers. It also has a built in beaver tail, which is something I personally don't find I've ever needed, but a Glock bite is certainly something I've seen other people have issues with.
Recoil has apparently been tuned quite a bit, at least for those that have the skill to perceive such a thing. I don't know if I'll be one of those people, but I was curious. You can also mix and match any of the current three Gen 6 slides with any of the receivers. Not something I need now, but an interesting change, as you can actually make a fourth "model" if you buy the 19 and a 17.
Lastly there is the grip texture (which seems nice) and the thumb index...which is stupid. Why they put it there, I don't know, but it's dumb. If they had just made the serrated texture in the take-down crotch and behind it, it would have been a better choice.