For starters, I get an extra hour of work in, not having to commute.

Next, while I do get distracted with home things, I am less distracted than I am from non-work things in the office (mostly my co-workers).

Next, I am better able to cure things that negatively affect productivity at home. For example, when I'm dragging at work, I start to avoid work or my quality drops. At home, I take a quick nap and then get right back to work fresh. Overall, the nap helps me be way more productive. Lunch takes way less time. Grab left overs out of the fridge and eat at my desk while working.

Finally, I am much happier because I am more quickly able to take care of critical personal issues and better able to balance work with the things that I want to do that a less flexible schedule prohibits, even when I am working more at home. For example, I play soccer at lunch, but then work later in the evening. I would not be able to do both if I went into the office because there isn't an opportunity for me to play soccer other times besides lunch.

The metrics that my employer has to measure productivity and results prove that I am more effective working from home, by a lot.