Most newer emissions type carburetor stuff would pop/backfire out the exhaust without one if their throttle was suddenly closed, like every gear shift. Some engines have a tendency to stall if the throttle doesn't come down slow. If you are a crude down shifter, with no rev match - just shove into gear, then you will have more drivetrain wear/abuse and should not get a lightweight flywheel.
If you don't have a problem with driveability or noise or crap into the atmosphere, then you don't need one.