Question about Zyxel Nebula NWA1123-AC PRO

What is the LAN port for? I understand uplink/PoE, but why does it still have a LAN port? The Zyxel NWA1123-AC PRO does not have a power adapter port, so you could use a normal LAN cable + power adapter if the power injector went down. So I absolutely need the uplink/PoE. So what do I do with the LAN port? Would this be the case if I use the NWA1123 as a repeater and then attach e.g. switch + additional clients to the LAN port? So for example: Modem <-RJ45-> AP1 --- wifi --- NWA1123 <-RJ45->switch <-RJ45->clients? Thank you.