It’s a mesh thing.
A battery powered Z wave device keeps a “neighbor table” of the addresses of its closest neighbors. Those are the ones that it will try to send its messages through. This table is built at the time that the device joins the network.
When you pair the device right next to the hub, it’s going to choose as its neighbors the devices which are close to it at that moment in time.
However, once you move it to its ultimate location, there might be other devices which would be much closer repeaters for it. In order to get the best network efficiency and the fastest message transmission, we want the battery powered device to have a neighbor table of its “true neighbors.“
Otherwise, if the neighbor table in the battery powered device is still the one that was built when it was close to the hub, then it may keep trying to reach devices which are far away, resulting in lost messages that then have to be sent again and again. These retransmissions are using up your battery life.
The zwave “repair“ utility just tells each individual device on the network to find its current true neighbors and rebuild the neighbor tables. At the same time, the hub charts some prebuilt message paths and passes those along, which also helps improve message efficiency in the future.
So it just realigns your network’s image of itself with the devices’ true physical locations.
Zwave plus devices have something called “explorer frames“ which will do this kind of update little by little overtime. But Z wave classic devices don’t all have this feature, so you can have a device which never gets its neighbor table updated. The repair utility fixes that.
So it’s not that one way is better than another. Sometimes you need to do a bench pairing in order for a device to exchange security keys with the hub, what is called “whisper distance.“ this is often true for Locks. But if you do a bench pairing, then after you have moved the device to its desired location, you just need to get the neighbor tables updated by running the Z wave repair.
However, if the device’s desired location is within one hop of the hub, then it’s going to have the same neighbors anyway. So the repair utility probably wouldn’t make any difference.