I never meant to say that the intern should not do such things. I just meant that it's not behavior to be encouraged on the workplace because it can have negative connotations that can hurt the social aspect of the team and/or can cause burnout which will inherently hinder productivity. If an intern wants to work 12 hours for any reason by all means let him. But if he's doing 12 hours + each and every day to basically prove his worth, there needs to be a limit before all parties come out losers in the relationship.