Similar in function to APCs, Transport Copters (often shortened to T-Copters) trade the ability to resupply other units for increased mobility.
Like APCs, T-Copters are capable of transporting one Infantry or Mech unit, moving them across any terrain without being slowed, thanks to their Air movement. Their inability to utilize terrain defense often leaves them vulnerable, however, so care must be taken as losing the T-Copter will also destroy any unit inside of it.
Unlike APCs, T-Copters cannot resupply adjacent units. Instead, T-Copters are able to travel over Mountains and Oceans, as well as not being slowed down by forests, allowing them to reach certain areas faster than APCs. T-Copters cannot sustain much small arms fire, only being able to take one attack from almost any unit before being put at dangerously low HP, so using them to block units will not last very long.
Like APCs, T-Copters are harmless on their own, so they can generally be ignored unless they are blocking the way.
Since they cannot resupply allied units, the only reason to specifically go after a T-Copter over other threats is if it is currently moving foot soldiers to dangerous spots, such as unguarded properties.