20 or so SSIDs beaconing adds up to a lot of airtime. Consider:<p><pre><code>  * beacons are sent at a low &quot;common&quot; rate, perhaps 6mbps
  * beacons still include the preamble and the DIFS before that
  * 802.11n&#x2F;ac get high bandwidth from aggregating multiple frames
</code></pre>
So all those trivially small beacons take little <i>bandwidth</i> but a significant amount of <i>airtime</i> (which is a significant amount of <i>potential</i> bandwidth for faster clients with multiple frames to send in one aggregate)<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Distributed_coordination_function" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Distributed_coordination_funct...</a>