6 Reasons Actors Use Doubes

Safety - Stunt doubles are used when a scene requires a dangerous stunt that the actor can't safely perform.
Skill - Stunt doubles are used when the actor doesn't have a particular skill needed for the scene.
Comfort - Stunt doubles are used when an actor is uncomfortable performing a nude scene or needs a close-up of a specific body part.
Availability - Stunt doubles are used when an actor is unavailable.
Physical condition - Stunt doubles are used when an actor's age or physical condition prevents them from doing much activity.
Contract - Stunt doubles are used when an actor's contract prohibits them from taking certain risks