You can use this e.g. if you are in an area with a weak 4G but a strong 2G connection. Usually your phone would prefer the strong - but slow - 2G connection, but with this tweak you can force the usage of the weak 4G connection, which is usually still way faster than a strong 2G one. Another example would be if you are in an area where your phone constantly switches between two network types, thus draining your battery. Simply lock it to one of the available ones to save your battery from draining from all the network switching.
Not compatible with eSIMs.