Many spatial analyst tools use the environment setting Mask which is a powerful way to limit a tools processing to a specific area. A mask can be a raster but it can also be features (vector data). I often use vector data as a mask, e.g. island polygons to say mask a raster landcover dataset I wish to process.
Just about every tool that takes a vector dataset as input will honour selections. But the Mask environment setting ignores selections, it always uses the whole dataset.
My idea is to enable the mask environment setting to honour selections on a vector layer if it is used as a mask for a raster processing tool (e.g. the CON() tool). If the datasource of a layer is used instead, then I expect all features to participate in the masking.
So in my use case scenario I have a global vector dataset of islands, I've selected a subset and I want only those to be considered as a mask, currently the selection is ignored and all polygons are considered a mask.