"When new mother Marissa Mayer took the reins at Yahoo then banned employees working from home, and Sheryl Sandberg, Facebook chief operating officer, told women to "lean in," the conversation about how to handle the demands of both home and work became impassioned."

Marissa herself does not believe in balance. She will literally work 24 hours a day, 7 days a week:

http://www.businessinsider.com/the-truth-about-marissa-mayer-she-has-two-contrasting-reputations-2012-7

More on a normal Marissa Mayer day:

http://googlesystem.blogspot.com/2006/06/marissa-mayers-normal-day.html

http://www.businessweek.com/stories/2006-06-18/marissa-mayer-the-talent-scout

She sleeps 5 hours a night. Geez.

Wow, that's someone who loves to work! I have often wondered about how much I could accomplish if I only had to sleep a couple of hours a night. I would definitely get an enormous amount done...right up to the point I keeled over at an earlier-than-I-should-have age?!!

Martha Stewart once reported that she slept only four hours a night!  Some people are just wired that way.  

Workaholics don't necessarily enjoy work more. They just don't know any other way.