In a roaming system, you must set the RSSI (Received Signal Strength Indicator) threshold, which is the weak signal strength that the radio will consider to be strong enough before the radio starts searching for a stronger signal.
Roaming is a limited use function, some people will need it, some people will not. This is a commercial function adapted to DMR amateur radio. Basically, that means you are driving from the south of the city to the north of the city, for example, there are 5 repeaters along the way. If you have been moving, the handheld walkie-talkie or mobile radio in the car will automatically switch to a channel with a strong signal and close to your repeater, because you are moving to a strong repeater in a geographic location.
But suppose you are using your handheld walkie-talkie/mobile radio and hotspot device at home, roaming will not help you, because your handheld walkie-talkie or car radio does not need to change the frequency or channel, so the signal is constant. Therefore, for some people, for example, you are traveling in a city, and you want your mobile radio or handheld walkie-talkie to automatically roam to a nearby relay. If a mobile radio with a roaming function is installed in your car, then It will be a good thing for you.
Roaming is like intelligently scanning for repeaters and using available signals to maintain the same TG. Regardless of whether the signal strength is strong enough, scanning usually stops on the carrier.
The difference between scanning and roaming is that scanning will continue to scan until a signal is received while roaming radio will use the repeater in the roaming list to connect and remain locked on the channel until the signal is too weak.