It doesn't extend the actual zigbee or zwave network but... Logically its offers a functional equivalency.
Hub Mesh is ingenious in that if offers the behavior as if devices was local even though they are on a different hub and on completely different networks. They do this by transmitting device events and states across IP networks to remote hubs that presents these devices as virtual devices that are logically and functionally an equivalency of a local device.
Since IP can go many kilometers (and certainly hundreds of meters/thousands of feet) it offers really nice properties for automations of devices that may at least those distances apart.
I now have three hubs in my mesh. I really dig it, i find it highly reliable. My only regret is that i didn't plan for this up front. Its a pain in the you-know-what to exclude certain zwave devices, and even more so if they are at a bit of distance from the hub. Thank lord i have that zwave stick -it makes it a fair bit easier when devices are troublesome.