Well, not all home users are professional network-engineers. For me there was a valid use for dual-mode. I owned a Cisco AP that used vlan 1 untagged for management and other vlans tagged for different WLAN SSIDs. I did not want to lock myself out of the AP management interface so I chose dual-mode 1 to solve my problem. Sometimes the machete works well in the hand of the user that does not know how to operate a scalpel
It's not just this, either. I AM a professional engineer and I can tell you as a point of fact that dual-mode is needed MUCH more frequently than it was in the past. For example, there is an IPMI/iKVM vendor where you MUST use a dual-mode analog for both the 'true' IPMI port
and the shared failover port, even when the IPMI/iKVM is configured to tag traffic.
Yes, even when it's tagging the traffic.
Because the IP 'heartbeat' sense and the failover motion itself does not tag the traffic. It can't. Because the failover side cannot operate with a tagged VLAN. And if you are using the shared port on the host with certain tagging modes, the IPMI will cease to function because it sees the VLAN tag on both the active and failover and reads that as 'both hot.'
Nevermind when we get into other stuff where it's a shared port that just doesn't tag period. Or my favorite, the one that won't tag until late in the boot stage, but also drops the IP if it can't ping the gateway while not tagging. (You know, because
that makes sense.) And that's not even touching on UBNT's utter incompetence.
Shitty, amateur, incompetent 'design' in "enterprise" hardware really has run rampant.