I use the Camera Lens Blur effect often, because it's awesome for creating realistic Depth of Field- when you plug a depth matt into it.
This can be a Zdepth pass from a 3D renderer, or you can just paint one up in Photoshop to use on motion tracked matt painting work.
Or mock up a simple instagram 'tilt-shift' treatment with a couple masks in a precomp (attached 4k example AE Project)
It's the most sophisticated spatial blur in the AE toolbox, and it is super CPU intensive!
Vote this up to get on the list of GPU accelerated Effects for upcoming releases :)
And Cheers to the AE Team for recoding the Noise Effect for GPU acceleration in the 2019 release! Another indispensable Render Hog effect, that I literally use on every comp I make :)

PS- I could not upload at .aep file here (?!), so I had to fake the extension.