it's for wireless links, for example. we have non-WDS link, so all clients on the other side have the same MAC address. but DHCP requests contain their real MAC address - that allows us to lease correct IP addresses. if "Use Src. MAC Address" is ticked, then only one user can obtain the address. something like that
p.s. also, it has meaning when using DHCP Relay, I believe
hmm, I'm afraid I don't understand what you mean. All my AP's have non-WDS links to clients. They all get dynamic IP's from AP-dhcp server where after I set this IP to a fixed one so they always get the same after disassociation and re-association.
The MAC address field is filled in the lease window of winbox for each client on that AP automatic by ROS. And they all have off course different mac addresses.
I have one AP where one client antenna is in WDS-station mode, so the real client PC behind is bridged to the AP. Both antenna and client PC get an IP address from AP-DHCP server. Both with their own mac address.
Since lease fields are usually always dynamic dynamic for me in 1st instance I never have to tick the "Use Src. MAC Address" box since ROS fills it by itself.
Only if I want to make sure a CPE gets a certain IP address (in pre-configuration, and thus in pre-association of CPE) then I fill the CPE mac address in the lease field I make. I tried with a laptop and saw no difference in ticking yes or not the tick box of this discussion.....