People enjoy tit torture for a range of reasons. For some masochists, the pain actually feels good – they experience it as very intense pleasure. For others the pain is unpleasant, but having their tits tortured makes them feel submissive and obedient, or makes the sexual activities they get onto afterwards hotter.
For sadists, tit torture presents a whole new range of ways to hurt their willing victims. It’s a thing worth exploring for anyone with any interest in pain.
Tit torture can also be a tangential part of other fetishes. Folk who enjoy human cow roleplay might enjoy playing with the idea of “milking” their lover, and a little bit of tit torture works well as part of play involving predicament bondage.