Leaving the transmission on helps in that you now have a way to keep the clutch... and it gives you an easy way to connect at the tail section.... the same way the driveshaft connects...and disconnect easily compared to some systems....You would probably use 4th gear... but in my case wanting to run an air compressor or other hydraulic pumps... ect... it it sometimes advantageous to have other speeds available without getting out of the proper torque curve for the engine....