For people who like doing other things, work already takes up most of their time and energy 5/7 days, and there doesn't seem to be much time for much else.
Be careful of calling this an ideal employee.
I, for example, tend to have a little bit of such a schedule, but what I work on at home is so much more exciting, making the job much more frustrating in comparison. Also, one is typically not allowed (or it is not possible) to apply all the really good ideas that one tested/implemented for the home projects at work.
Thus, the kind of employees who apply such a pattern are often very, very passionate about programming - but this kind of passion often makes them
- more frustrated at work (i.e. they might be cynical),
- less subservient (they often know better - from their "night work" - that a requirement makes no sense, and may be vocal about it),
- very opinionated about their "technological taste", not necessarily fitting the technological taste that the employer would love to see in the work (they have seen a lot more programming techniques).