You will understand what the Dehaze Filter is for when you need it. It's not a tool that is used on every image. It's in the Effects panel because that's where Adobe decided to put it. Is there a problem with that?
You can also use it to enhance mist or fog. So I guess that makes it an effect.
Dehaze is different because, according to Adobe, "The Dehaze technology is based on a physical model of how light is transmitted, and it tries to estimate light that is lost due to absorption and scattering through the atmosphere." So there's an element of content-aware scene analysis at a level that's beyond what Clarity does.
It's probably not enough to describe which tonal ranges Dehaze changes, because I think Dehaze varies what it changes depending on whether it thinks an area is hazy or not. Dehaze will affect hazy/background areas more than non-hazy/foreground areas, where Exposure/Contrast/Clarity would adjust the entire image the same amount.
One reason it's in the Effects tab is that Adobe recommends getting the Basic tab as correct as possible (especially White Balance) before applying Dehaze. But also because it can create a haze effect if you use negative values.
That's a good explanation!
Appreciate your input.
Dehaze defintiely seems to assess the image and apply more "haze / flare" around light objects when setting a negative value, and presumably remove "haze / flare" with an emphasis on light edges when applying a positive value. It also seems to apply a saturation boost, which clarity does not, as far as I can see....