If you turn off 2.4GHz in the Apple Airport Extreme, it pops up an alert that says
Turning off 2.4GHz Wi-Fi networking on this base station can adversely affect the overall performance of your network.
I ignored the message and turned off 2.4GHz. I have not experienced any issues, but what "overall performance" problems can happen here? Is Apple referring to problems with range, device compatibility, or something else?