What is "Creative sizes (Beta"?

How to understand this data?

[ken_b]

I've tried to find more about this on both AdSense and AdWords and haven't found it.

I don't know when this appeared, but there is a link to "Creative sizes (Beta)" now.

Click on it and you get a list of ad sizes. The first on the list is "Dynamic".

What does the Dynamic listing represent?

At first I thought this is where we see which ad sizes appear in the new "Custom Ad sizes" ad blocks? But I haven't set up any of those.

Then I wonder if this also applies to using a 336x280 and getting the smaller 300x250 ad size served in that spot.

But I see ad sizes listed that I'm not using anywhere, like 250X250.

So what does this new feature/tool tell us, and what do we do with the new knowledge?

.

[netmeg]

Where is it? I would think Dynamic means the responsive ads that change depending on viewport but maybe there's something else. They're definitely busting out the new stuff a mile a minute.

Edit - I found it, it's in reports. I suspect that's responsive ads, but the numbers don't add up so I'm not sure. I see sizes I don't normally run too, but I assume that's from the responsive ad too, if someone views it on an unusual viewport.

[ken_b]

Click on any performance report link and it's in the list on the left.

Right under "Ad sizes"

Added:

Yeah, I can't make sense of the numbers yet.