I'd be interested in what the Kubota manual recommends.
My thought on leaving the clutch disengaged (using the hook) was for long term storage of the tractor, to keep the clutch plates from bonding (rusting) together.
Never would I want to have the clutch disengaged while the engine is running. Seems this would run the risk of removing clutch facing. Too close to "slipping the clutch" which wears them out quickly. But then people blame the tractor for the clutch wearing out, and don't know they have done it themselves.
What does Kubota say about this? I may have it all wrong.