It's for recording videos I'd expect.

Although nobody wants to watch a video like that either.

What if it boosted your frame rate and saved your battery?[1]

The blurry areas could be rendered at lower resolution then blurred to the final screen. I read an article where a 2D side scroller used this technique to good effect on its frame rates.

3D would require a serious mathematician to make the various edges match well enough to not be offensive.

EOM

[1] A Macbook Air that happily runs 6 hours on battery will run about 90 minutes playing minecraft.

This looks far more computationally expensive than without shaders.

That side scroller benefited because it could just draw the background/foreground sprites at a lower resolution before blurring. You wouldn't be able to get that luxury easily with a 3D game.

I can't speak for all games, but I find my fragment shaders dominate. That is compute power related directly to the number of pixels rather than polygons.

If I can render objects in the distance at 1/3 the spatial resolution, that is 1/9th the fragment shading, times a much reduced texture bandwidth since I'll be using a lower resolution mipmap.

I'll still have to composite it back in to the full resolution frame, but if that operation is faster than my fragment computations it would win.