I’ve seen discussion posts that mention using masks is “expensive” but I can’t seem to find exact information on why exactly? ref

In the official docs about performance tips it says,

Masks can be expensive if too many are used: e.g., 100s of masks will really slow things down

From what I can infer it seems related to masks applying a filter and it breaks the batch rendering. But why does it say it’ll only start causing performance issues when I reach the 100s?

Also something I’m not sure about is how does masking actually work? Does it compute content outside of the mask then discard the pixels, does it draw it but hide it under some transparent sheet. All this is a mystery to me and there seems to be nothing concrete written down.