I received a few electronic solicitations to get a free rain barrel from my local water district which I promptly ignored. As I've noted before, they aren't a particularly good investment for southern California.
However, there are a couple specific exceptions to normal situations in which a rain barrel might be a good use of resources in our climate. One of those is when it's used as a surge tank. Surge tanks might sound complicated, but the concept of operations for a rain barrel used as a surge tank is not that different than a rain barrel used as a reservoir.
The picture below shows a schematic rain barrel with a hose spigot located at its bottom. Roof runoff goes into the barrel, and depending upon whether the spigot is open or closed and the rate of rainfall, the barrel drains or accumulates.
The barrel accumulates and stores excess water that can't drain fast enough when the rainfall rate surges, thereby smoothing out the rate of water delivery. This allows you to transport the water across impermeable parts of your yard and then allows it time to to soak in to the garden instead of run off.
Depending upon the collection area of your roof, the rate of rainfall, the rate of drainage, and a few other things, it may be possible for surge tanks to be quite a bit smaller than rain barrels which would mitigate the visual impact of a rain barrel in your garden.
Note to self: There's a calculation to be done here that I hope to get to later.