Classic correlations: a big favorite's moneyline with the game over (blowouts add points), a QB's passing yards with his top receiver's receiving yards, or a first-half line with the full-game line. Historically some books mispriced these badly enough that correlated parlays were a genuine edge; modern SGP engines price correlation explicitly, though imperfectly - measuring their haircut against your own dependence estimates is the modern version of the old edge.
Per-leg prices for game lines and props across books come from the standard endpoints, giving you the independent-multiplication baseline; the SGP demo shows correlation-adjusted pricing on live games for comparison.