Guild Wars 2

Does this thing even do anything? I notice no difference having it in any position on the slider.

It does. The easiest place to see the difference that I know of is in the room where you fight Rhendak. The end of the JP in Kessex probably works too. With the slider all the way to the right you can get the camera outside of the room. With the slider around 4 ticks back towards the left you will no longer be able to do it and instead the camera just gets pushed against the wall instead.

find a tree in Lion’s Arch.

set collision sensitivity at default.
Move the camera so that it hits the tree and zooms in on you. Now move the slider and see how the camera goes through the tree

I’ve also found that testing it along the battlements at Fort Mariner (south Lion’s Arch) works well. If you have it set to one side (I think the left-most), you’ll be able to angle the camera down across the battlements, but not have it zoom in. That is, you’ll be looking up at your character from a bit of an angle below the battlements. Then you can swap it up to max and see how the camera snaps into position.

There’s also various wooden posts around places like Lion’s Arch that you should be able to test it on. Place one of them between your character and the camera, and mess around with the slider.