David, normally I leave the handles in the sheet in service, (normally for constant trim), and off the not in service
winches.
Therefore, I leave them on the low side
winches. (note my main is sheeted in either from port or starboard).
See photo bellow
Once someone is handling the sheets its up to them how they prefer..either in the pockets or on..but generally they stay on all times.
If you are sailing along in a relaxed manner, leaving them off is good, but all depends on your habits..even cruising I leave them on.
In an emergency the removal is quite fast.
