Wi-Fi Assistant - definition

Wi-Fi Assistant is an option provided by the phone manufacturer so that the device can switch to an efficient option in terms of higher traffic or poor connection. There could be variations based on device or OS(Operating System).
If the device is connected to an accessible WLAN zone and the data bandwidth is poor then it'll switch to data mode automatically, in another case, if a device is working as a hotspot and too many devices are drawing most of the bandwidth so that providing device is having trouble getting sufficient bandwidth then this feature will automatically limit the user or bandwidth.