Mike Bostock knows far more about data visualization than I do so I assume there are good reasons for choosing this presentation. But it strikes me as hard to think about, so I must ask: when is stacked+packed circles a good choice?

The drawbacks to me seem to be:

- At any given point on the x-axis, the associated height of the pile is partly taken up by circles but is partly space lost to circle packing. This proportion is hard to estimate visually.

- Because circles extend in the x-direction, they contribute to height over a _variable_ time range. E.g. WaMu is still the tallest circle at the 2010 line. It's a bit like a kernel density plot where the _kernel_ is data dependent.

Because of these effects taken together, though it's tempting to think of the profile of the pile as a smoothed average of the rate of bank-failures, but this is pretty misleading, which I suppose is why there's no labeled y-axis.