Manual says don't disconnect battery with engine running. Why not?

[stuckmotor]

Thanks again, guys and for the private reply also.
Stuck

 

[TemporaryKubotaOwnerMark]

I ran my MF 261 for a couple of years with a cheap replacement battery terminal clamp that occasionally slipped loose from the positive cable.

Best replacement: military style terminals.

Order custom cables to go with it from this place.

 

[tcreeley]

I sold an old Nissan Sentra one time that had been sitting and the battery was dead. A guy showed up and bought it on the spot. I had no cables and he didn't either. He took his vehicle battery and swapped it in. Started the engine, and while running, he swapped the old battery back in. His buddy drove his vehicle, and he drove the Sentra, all unregistered, un-insured away. Life in rural Maine.

I'd never seen that done before.