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MAC filtering can reduce the amount of traffic the router reads beyond the header, but the radio is always receiving signals, amplifying them, and passing them to the modem. Any non-802.11 data is simply ignored. For 802.11data, the modem demodulates and passes to the router. The router then does its thing, passing the traffic on, assigning an IP, or whatever is requested within the configuration restraints.

Any power or equipment savings is miniscule.