I've had employers tell me to work more hours so they could bill our clients more. I was naive, and asked why, as my components didn't require all-day debug sessions at client sites, and I regularly hit my milestones. I didn't understand the perverse incentives that come into play when consulting. No doubt they wanted me to work on something; but all they saw was the dollar value I was worth. In the time I would have spent at the office, I arguably put it into something more productive (long-term), such as working on side projects, or practicing a musical instrument.
These days I consult at a strict 30 hours a week. I have workaholic tendencies, so I'm on a rest cycle WRT work.