There is rarely any need to use a second hub, though I am sure Hubitat would love it if you bought one regardless. 
(Segregating problmeatic Zigbee bulbs to their own network is one reason you might. Running untrusted custom code on one hub only is another. I got my first "second hub" so I could do testing and development on it without bothering my "real" hub. Some people like to split the work between multiple hubs for various other reasons that may or may not be grounded in reality or personal preferences.)
@Cobra's advice is basically what I did when I got my second "second hub," which I did to isolate as much as possible all of my lighting-based automations and devices to this one hub (again nothing most people would need to do, but I wanted these to be as fast as reliable as possible while keeping some custom apps and chatty devices like power monitoring ones on my "main" hub). There are no selective backup/export and restore tools, though staff have hinted that they are experimenting with ideas like this; the hub database has all your hub/location information, plus apps and devices, including complete information for Zigbee devices and not much more than node IDs (and names) for Z-Wave, with the rest of the information you need to actually use the devices stored on the Z-Wave radio itself (built-in to the C5 if you're in North America, so no good way to move, unless you're using an external device like a Z-Stick or in another region--and then there are third-party tools that can back up/restore this, but again it's basically all or nothing).
Like him, I'd also recommend HubConnect over Hub Link, assuming that you are OK with the license and the need to run third-party code (Hub Link and all drivers are built-in and officially supported in that sense, but staff have even recommended HubConnect to others in the past and lots of people are using it with success). It's a bit newer and more powerful, and it supports more devices (and doesn't create annoying "virtual shadow devices" on the host hub), so I'd at least give it some consideration even if you decide not to use it.
