My direct commute would be about 10-miles but the shortest-fastest is about 12-miles - which I do going home.
In the mornings I typically take a rather less direct, but more enjoyable, route of 22 to 24-miles.
I guess it depends upon why you commute by bike. My primary reason is that I like cycling and doing it as a commute is the best way of it being part of my normal day-to-day life without using up lots of time. Cycling as a means of transport, saving money, not using a car etc is all secondary to me.