Guns in Movies and TV shows

[pulledagroin]

I know nothing about guns.

In many TV shows and movies, when someone has a handgun pointed at someone, they will pull the little hammer back at the end. This is uaully used to intimidate someone further, saying "Yes I'm serious" or something like that. Also, this is usually after a few minutes of already having the gun pointed at the person, leading me to assume the gun could be used without doing it.

Does this action serve any purpose other than intimidation? It has never made sense to me, someone please explain!