What Do You Use Your Rain Barrel For?

People sometimes ask me this, and I have a difficult time answering.  I think a lot of people use their rain barrels to store water from rainy periods for use during dry periods, but I haven't really had that option much, since I just got my rain barrel in July.  Plus, the advice I received from the company rep when I got the barrel (see A Rain Barrel!) was to not hoard water - empty the barrel every week or so.  (Though I can tell you now: this is not going to happen.)
But my barrel has a few additional benefits.

1. less water in the soil around my house during very wet periods
2. less water running through my backyard during very wet periods
3. R thinks it's fun to turn the spicket on and off
4. reservoir to moisten the soil around my house during very dry periods. 
5. less high-speed, contaminated rainwater runoff flowing into the local waterways

The last one is pretty important to me, but difficult to explain in casual conversations.

If my house weren't standing in its way, rain falling on my property would pretty much all soak into the ground, where some of it would filter down and recharge the groundwater supply, and some of it would later evaporate back into the air.  But because my property is occupied by a house, a great deal of the rainwater that falls on it is fast-tracked over the ground's surface (both because there's less surface to soak into and because the turf is disturbed and less permeable than in its natural state) and onto the street, where it can pick up trace pollutants and animal by-products before being dumped at unnaturally high speed into local waterways.  The negative consequences of this include diminished groundwater supply, eutrophication, erosion of my property and riverbanks downstream, harm to flora and fauna in rivers, and increased sedimentation and pollution in the bay.

One rain barrel makes very little difference (see Rain Barrels for some fun math about how little water a rain barrel actually catches), especially if I don't empty it before each rainfall.  But it makes me feel a little better and is more effectual than trying to convince politicians to redesign/rebuild our storm drain system.  (The most convenient and efficient solution for their citizens.  I think.)