Conventional wisdom tells us that we should separate our lives and our careers to keep appropriate work-life balance. There is nothing wrong with this advice as it serves a purpose. However, what if you like your job and find meaning in the work that you do. Then it becomes a way of living in the world, seeing the world, and making a living in the world. It is a pleasurable experience that means more than a 9-5 paycheck.
Consider the difference between a person who likes their job and someone who doesn't. A person who likes their job enjoys coming to work, is committed to their tasks, thinks about ways to improve their effectiveness, seeks growth opportunities, and integrates it into part of their identity. Those who do not like their job seem to compartmentalize their work, do the minimum, seek to get out as quickly as possible and have little vested interest beyond pay.
People who are actively engaged integrate their work into their lives and identity. It becomes something they simply "are" without stumbling over their career or identities. When they wake up in the morning they have positive images and impressions of the work they do. Even though the are natural up and down cycles of commitment they maintain an interested stream through it all.
For example, a person who loves designing electronic equipment will take intrinsic pleasure in playing with electronics, buying electronics, thinking about electronics, learning about electronics and/or inventing new devices. They do this because they find pleasure in the type of work they do and integrate this into their lifestyle.
On the contrary a person who doesn't enjoy their job thwarts that identity as soon as they walk out of their office in afternoon. The don't think about their occupation in the evening, show low levels of commitment, and generally disdain going into work everyday. They are externally motivated and if it wasn't for the money they wouldn't bother going.
The difference of the two can add up over time. A person who is uncommitted is likely to bounce from job to job and be generally negative in their workplace disposition. Someone more committed will find more interest in their work and stay longer at any particular organization. They will learn more and do a better job then someone not mentally engaged in their work. Integrating your work into your lifestyle is more about identity and interest than it is about overworking.