When parsing a polygon, we always validate the geometries, like checking whether it's self-intersected among other sanity checks. (S2 already has optimizations for this rather than using the naive O(n^2) algorithm). The dependency graph given by CPU profiling shows this validation takes 80% of the running time for polygons with thousands vertices. If there is already an index on the geo field, this validation is guaranteed by the index, so we can skip it for stored geometries.