Here's a good article in regards to why its good to have a repeater even if it's close to the hub.
This is the key takeaway from it though:
Lock manufacturers have to meet two conflicting consumer demands. First, people donāt want to change the batteries In a lock more than once a year. Second, they want the lock to almost instantly respond when someone enters the code or runs an automation. (Basically, no one wants to be standing outside in the rain while they wait for the lock.)
OK, the normal way to extend battery life on a Z wave device is to make the device āsleepy,ā that is, it is inactive most of the time and just wakes up periodically to see if anything is going on. But that doesnāt work for locks, because it would make the wait time Longer than people will tolerate.
So zwave came up with ābeamingā which is A way to have a repeater which is close to the lock hold its messages and re-transmit them the instant that the lock wakes up. Thatās very different than the pony express paradigm. Instead of just trying to get the message from one place to another as quickly as you can by passing it from rider to rider, when the message gets to the last stop before its destination, it is held there, and is soon as that station realizes the lock is awake, they tell them that they have a message waiting. And again, this was optional when it was introduced.
So for Locks, you want to always make sure that the repeater closest to the lock, ideally within 10 or 15 feet of it, supports beaming.