I know what pattern draft is and it's usefulness in removing castings from rigid moulds. That's the definition you can find anywhere.
My problem is when you sand cast. Sand casting is the most common amateur metal casting technique, with lots of YouTube examples. Yet all the decent examples have a draft incorporated. Since you destroy the sand mould when extracting the casting, I can't see any benefit from a draft. It just adds an unnecessary level of complexity when designing and making the pattern. Any shape could be successfully removed, so what's the point of pattern draft in sand casting?