I have 4-5 different routes to/from work all roughly the same length. There's a small lake between home and work, so it's about which way around it, plus whether I have places I want to go on the way home.

Of those choices, I'll use the same one going to work about 90% of the time, using an alternate once in a while to break up monotony. But I'll vary the ride home greatly, using any of the routes depending on errands that i want to do, or simply based on whim. By the same token, if it's nice out, I'll turn my 6 mile ride home into a longer loop between 15 and 40 miles.

So going to work it's all business, but going home is about the ride about half the time.