Thought I'd take a look at the custom Adsense block size feature that Google has introduced.... and sure enough, as you go about creating the block code, there is a message to the effect that as it is unlikely anyone is creating ads to your custom size there might be a fall-off in your Adsense income.

Really? That has to be obvious to a blind man.

So why would Google provide an opportunity for webpages to carry custom block sizes when no ad inventory exists for that size?

It seems at first blush to be a nonsense so what am I missing?