Sounds like...
..this is a setting to keep the net away from specific machines inside the network. However, I see on the linksys site, this description
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Wireless MAC Address filtering is the best and simplest form of security.
Wireless MAC Address Filtering allows the Wireless Router to reference a list of the MAC Addresses "allowed" wireless users, and only allows the "allowed" MAC Address access to the Wireless Network, any computer not on the list is dropped.
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So at least for linksys, it appears that while it is poorly documented from what you've seen, that is where you lock the router to specific machines to allow access.
I will choose a path that's clear. I will choose freewill.