In computer networking, a WiFi access point (AP) is a device that allows wireless devices to connect to a wired network using Wi-Fi, or related standards. The AP usually connects to a router (via a wired network) as a standalone device, but it can also be an integral component of the router itself. An AP is differentiated from a hotspot, which is the physical space where the wireless service is provided.
Most of the routers selling on the market are already having WiFi function. A quality WiFi router could cover a small house and be sufficient for your daily use as well as streaming audio. However, when comes to a regular U.S house with different rooms and levels, the single WiFi router setup may not work properly as the router's signal range is limited and won't be able to cover the entire house.
Adding WiFi access point(s) can help to extend the range of your home network and make sure a good coverage of the WiFi network in every all area in your house. For streaming audio, you will have a more reliable connection between Lightning device, music server and control point which could improve the reaction speed on your control point and reduce drop out when playing high resolution music files.