it depends. Some transmissions are different. I know some of the transmissions, specifically the hydro-mechanical type manually selecting a gear reasults in a higher line pressure that helps reduce slippage off the line, but will also result in firmer shifts as you manually select the next gear.
Like it was mentioned before, don't put the transmission into a gear with the engine reving higher than idle, its not good for it. Just like selecting a forward gear while moving backwards and vice versa.
manual gear selecting can be helpful and even benificial to the transmission especially under severe service like towing a heavy trailer or snow plowing, two things that will not likely be done with your contour.
