It will usually depend on the situation. I have had to work extra because it had to be completed before the end of the day or week. Sometimes I have worked extra just to make some extra money.

1. You like to work 2. You feel responsible for your work and the work needs to be finished 3. In client facing roles, there are times when the work requires to go by the timing of the client rather than yourself 4. You want to finish the pending work before the weekend maybe. These are the situations I have faced :)