What happens to a man that masturbates almost all day but in the masturbation prone position? not using hands only humping a bed

All day?: You have indicated that you are asking about someone you know. A developmentally-disabled or mentally ill man may do this, and if he's not otherwise able to be productive, it's probably making him happy. A grown man who seems like he should have something more to do with his life may have an obsession with erotica and need mental health care, but he's the one who must seek it.

The man wastes time.: Frequent or exclusive prone masturbation places significant pressure on penis & nerves at its base & may cause numbing to arousal / pleasure wi other positions. Seek help for delayed orgasms, erectile dysfunction or inability to achieve orgasm in other ways. Masturbation all day = sexual addiction. REF: https://www.healthline.com/health/healthy-sex/prone-masturbation#effect-on-sensation