You can manage 50 people through the strength of your personality and lack of sleep. You can touch them all in a week and make sure they’re all pointed in the right direction. By 150, it’s clear that that’s not going to scale, and you’ve got to find some way to keep everybody going in productive directions when you’re not in the room.
http://www.nytimes.com/2010/01/31/business/31corner.html