Access control by MAC address is a common feature on routers, including WiFi routers. In my (personal) opinion, this is paranoia and overkill. The intent is to keep out a talented hacker who has captured enough packets to defeat the WAP security and learned the WiFi password. Mine is 25 characters lone and would take something like 4 billion years to guess. But, if instructions on the internet can be believed, someone with the skills, equipment, and time could sit outside my house and break into my WiFi network.
What do they get once they are in? Internet access, of course. But surely someone capable of this already has far more internet access than my poor Spectrum account. Hack into my Orbi. Well, there's a different 25 character password on that. Hack into my Windows 10 or Linux machines? They have firewalls that reject connections. Stream TV? What, they have a TV in the car parked outside my house?
All I see, as you do, is the downside. Once Access Control is activated, when the wife invites someone over who wants to show her something on FaceBook and asks, "what's the WiFi password".... oh, dear. Won't connect. When I get home, it will be cold supper for me! As long as I am the only person adding devices, then I can manage Access Control. Change settings, add device, change settings back, etc.
As far as I can determine, Access Control covers both the primary WiFi and the Guest WiFi. "Control" means CONTROL.
Others will probably have more 'balanced' viewpoints.
