Inline styles cannot be cached, cannot be overridden without !important, and re-download on every page. Past a few hundred, they are measurably larger than the stylesheet they replaced.
Impact is importance multiplied by the confidence tier’s weight — SPECIFICATION 1.0, RESEARCH 0.7, EMERGING 0.3, EXPERIMENTAL 0.1. Two rules backed by the same class of evidence therefore always carry the same weight, which is what makes the score reproducible rather than hand-tuned.