1A2R switch is a RF and PTT router which routes one amplifier between two radios.
Switching is based on the PTT signal using the first one wins principle.
You can disable the PTT switching for each radio independently by flipping a switch.
Once you connect it, you will not need to rewire the setup and your amp is routed premanently.
In the case of failure while running SO2R, you can switch the amplifier from radio B to radio A as a backup.