Hi _Ross_
They mean exactly what they tell:
None: No special.
In Cargo: The unit will start the mission in cargo of teamed vehicle.
Flying: Flying! (Only works with what usualy can fly, planes, copters, etc).
In Formation: Unit will be in group formation (Though You can pretty much use the "F2" key to do this manually cos if You place a unit close to the other, (from the same team) they will team up automatically nomatter if You picked "None" or "In Formation".) Which in the end is a pretty useless option I would say. Correct me if I'm wrong!
cr u n c h