I think the most compelling use case is a separate guest network (which is firewalled from your normal network; some wireless access points tout this as a featu

I think the most compelling use case is a separate guest network (which is firewalled from your normal network; some wireless access points tout this as a feature). Power users might also run a VPN and allocate a subnet to VPN clients. There are also home automation standards that put all your devices on a separate subnet.