Uses for negative light values?

It’s interesting how Cycles can use lights with negative values. I get how it works, and it makes sense, but the big question is this: Can you think of a use-case where you’d want to actually do that?
I mean, other than “I want this to look weird”, and “Hey, look at this negative light” are there any cases you can think of where using this physical impossibility would be helpful for achieving an effect.
I’m having trouble coming up with any, so I’m curious.

Once I’ve used negative meshlight for faking soot on a surface. I needed black blur around animated text, but was lazy enough to bake it to an image sequence mask.

Works great in combination with cell shading / stylised anime / cartoon look.

You can compose the contrast of a scene in a way a photographer can only dream of.

Ooh, I hadn’t thought of that. I imagine you could use a negative light coming from the direction that is already meant to be in shadow.

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It’s a bit like post exposure in a photo lab, but before the shot is taken. LOL