Summary: This feature would allow you to use a group to clip a layer, so the resulting transparency of a group of layers would affect the transparency of the layer being clipped.
Usage: First off, I have hundreds of psd files from photoshop that use this feature, so I can't use any of these paintings inside Affinity because that feature is not supported (This feature is kind of a show stopper for me, since I can't port all of my older files over to Affinity)
And second, it's so useful for a non destructive workflow, many times you want to say paint a bunch of different characters on separate layers, and then apply a soft layer of fog to all the characters. So you group all of your character layers, create a new layer that has your fog color set to a low opacity, and then clip this fog layer to your group. In the current affinity workflow, you'd have to flatten all of those characters to a single layer, which means making edits to your characters later on become a lot harder.
Thanks!
- Neil