as an employer i value a healthy and balanced work ethic and a frienly and cooperative work environment.

personally i don't mind if you prefer to work more hours, but i'll be watching your performance. if it doesn't scale with the number of hours you put in then you'll have to cut down. also if i get any complaints from anyone else in the team. i can't have your performance demoralizing everyone else, because in the end it is the performance of the whole team that matters. i also won't be giving you extra opportunities for promotion or raises, because that would be unfair to others who can't work as much as you. again, doing so would be demoralizing for everyone else.

case in point, there is a company where anyone working more than 20 hours a week got reduced pay for those extra hours.