Zigbee and Wi-Fi use the same frequency band (2.4 GHz), but Zigbee does not use any Wi-Fi bandwidth to control the lights. So it doesn't matter if you have 1, 10, or 50 lights and accessories — you’re not using additional Wi-Fi bandwidth.
This is especially important if you have lots of lights or if you want to sync your lights to your TV, gaming setup, or music. Wi-Fi lights may lag; Zigbee lights won’t.