A spotter also spots targets for a gunner (for instance on artillery) they will give distance and position information to the gunner so targets can be neutralized quicker.
Fuzzie: No what happened?
Inspector Purple: He was found dead hanging from a tree at the city park. His pants around his ankles and his dick in his hand. Bottles of lube and tons of porn were strewn about. It is believed to be an auto ertoic asphyxiation death. He could have been saved if only he would have had a spotter.
Fuzzie: Spotter? What is a spotter?
Insepctor Purple: You know, kind of like "swim with a buddy". Have somebody there to cut you down before you die. It has to be a good spotter though so you can be sure you achieve your intended goal.