Nothing. I do this. I think the AC-Lite even has it's own DHCP, but I'm using the ISP router for that personally.
Usually the ISP router just sucks at wifi, but I have seen ISP routers which have only 100mbit/s uplink ports when the internet connection is higher. In that case you'd want a custom router also. Or if they ship some router with some features you dislike that you can't disable (like public hotspots, unpatchable insecure config interfaces, etc.)
Usually the ISP router just sucks at wifi, but I have seen ISP routers which have only 100mbit/s uplink ports when the internet connection is higher. In that case you'd want a custom router also. Or if they ship some router with some features you dislike that you can't disable (like public hotspots, unpatchable insecure config interfaces, etc.)