It's not a typo - and I don't think it's about partial engagement either.
The L5450's pto clutch is disengaged by lifting the lever, and a push-button latch holds it there. While the lever is up, there's heavy clutch spring force against the release bearing and against the flanged crank bearing. On some smaller tractors with that setup, there have been reports of the constant force eventually causing crank bearing or release bearing failures. Hence the recommendation is not to leave the pto clutch disengaged for long periods (hundreds of hours). It's easy to overlook, because the lever needs to be raised for starting the engine. It's good to get into the habit of lowering the pto clutch lever after starting. If you don't want the pto to turn, slip the pto gearbox into neutral.