I just tried this function, and one thing surprised me a bit: When turning the "Gamma" to the right, the image turned darker. I guess this may make sense in a print context (increase gamma -> more ink to the paper), but in relation to photo and video stuff, I would always interpret someone telling me to "increasing gamma" as "make it brighter".
Then again, Affinity seems to always start with a white background, so maybe I should see things from a print perspective when working with Affinity? I mean, what's the general philosophy one should expect across the entire Affinity application? Print (subtractive color theory) or Screen/photo/video (additive color theory)?