I would think that the screw off barrel is just so a hobbyist doesnt have to tear the tank apart to upgrade the barrel. Like upgrading a tamiya Centurion with my drop in 105mm L7 gun barrel Im making. You have to take the top off and unscrew it from the recoil mechanism. And Tamiya made it easy on that tank model.
Taking it on and off all the time to transport is a bad idea.