That is an easy one for me to answer, my job is just next door, similar to Cecil's. It is easy to get distracted by things that I see that need doing as I walk passed them. While in the car on the way to work those are out of sight if not out of mind.
Another factor is that I seem to go next door less prepared because it is just a short walk if I need something which then leads back to the first problem, not to mention the time loss from just walking around. I am not complaining, it is just that there seems to be less distinction between work and home when you work at home.

1/4 & 3/4 acre ponds. A thousand miles from no where and there is no place I want to be...
Dwight Yoakam