I've been working from home once a week in the past couple of months, and noticed that I spend more time working at home than I do in the office. For example, if I work from home, I'd be working from 8am to 6pm (with a few short breaks for lunch and etc.). If I go to work, I clock in at 8:30am (commute) and checks out at 5:30pm sharp.

In a way, my employer is getting an extra 30-60 mins out of me for the days I work from home (assuming that I'm as productive working from home as I am at the office, which I believe is to be the case).