What I found myself and found confirmation by the Siggraph Video of John Daro on the official ACES YouTube channel (https://www.youtube.com/watch?v=zjZk46EdR7g) is, that negative values do strange artifacts with certain operations. For example a Gaussian blur in Aftereffects can make big black splotches which (when measured by the colorpicker) are negative values. So I took John’s advice to convert to cct before such operations. And that sometimes works. But now I wonder:
Why does that help? I suppose because the negative values get clipped by the transformation to cct. So as a consequence they are lost.
So far I haven’t seen a visual problem with that, but given that the negative values where a correct result of the transform (because there where values outside the gamut of the new colorspace) the will not come back when going back from cct to linear/AP0.
So can someone shed some light upon that topic?