SSN???

What would be the benefit of having another persons SSN? Say... they moved into your house, used you for three months, and then up and left to go fulfill themselves without paying a dime. Maybe they happen to leave a bunch of job apps behind with their SSN on every single one... what could I do with it to benefit my life personally?

I know where he lives, but I don't know his phone number. But i can figure it out with his address. I've done it before.