It can last a good four hours.
    It's not interrupted once a month.
    It's safe to do it anytime of the month.
.   You can cheat if you don't know how to do it.
   You can do it in public and not be embarrassed. 
   You can do it with several people at the same time.
   You don't get jealous if your roommate does it loud.
   You can be proud to finish sooner than your roommate. 
   You don't get tired if your roommate does it day and night.
   You don't care if your roommate has done it before or not.
   You don't need to lie to your roommate about his performance.
   You don't mind that your roommate has done it with members of   the same sex.
   You can do it with your roommate and still be friends afterward. 
   You can do it with your teacher and not be friends afterward.
   You can do it with teenage students as a part time job.
   You can do it with college students as a full time job.
   You don't need to wait ten months for the results.
   You don't feel guilty about doing it alone.
   You don't have to pretend you enjoy it.
   You can eat or sleep while doing it.