Closeup photo of a full cheek snaffle bit in horse's mouth with cheek fitting in keepers to stabilize the bit in the horse's mouth.
Full cheeck snaffle keepers are slightly safer if they surround the entire cheeckpiece instead of just the buckle as shown, but are faster to put on an remove if attached as shown.
Full check snaffles can be used with or without keepers, but behave differently in the mouth. Most horses prefer the stability that the keepers provide and many believe stabilizing the keepers keeps the bit safe from catching on things.