With the changing of the seasons, I've noticed a variety of new threads discussing foul-weather/"beater" bikes as contrasted with fair-weather/"nice" bikes. Since I'm a bit suspicious of the whole notion of a "beater" bike (the red-headed stepchild in the family), I was curious about when, and why, you would want to keep and use one. I'm assuming that the basic criteria for being a "beater," broadly speaking, are:

1) Worn, old, or otherwise abused frame, wheels, components, etc.;
2) An unwillingness on the owner's part to lavish much time or resources on maintenance.

My question, then, is this: Under what conditions would you want to use a bike that meets these criteria? If you use such a bike, why? It's pretty clear, for instance, that you'd have good reason to use one if you commuted to work in NYC and had no alternative to locking up your bike outside. I can store my bike in my office, so I don't face this kind of problem. And I don't think of my commuter bike (which soldiers on through New England summers and winters and everything in between) as a beater at all.

So: Why a beater?