From the CLI guide it says,
Do not enable this option for virtual APs configured in bridge forwarding mode. This configuration parameter is only intended for use for virual APs in tunnel mode. In tunnel mode, all packets travel to the controller, so the controller is able to convert ARP requests directed to the broadcast address into unicast. When a virtual AP is configured to use bridge forwarding mode, most data traffic stays local to the AP, and the controller is not able to convert that broadcast traffic.
In the past this means that if you enable that on a bridged ssid, things break. Devices connect then after a while disappear from the network, until you reboot them. If that parameter is overridden or ignored when the ssid is set to bridged, that is good.