Ratings are objective, without specific player, team, and regional.
Ratings are verifiable and repeatable.
Ratings are comprehensive, requiring assessment of all selected criteria.
Ratings do not forget old games.
Cons
Formulae criteria are subjective (some use just scores, some use margin of victory, some include auxiliary game data, such as hits, interceptions, lead changes, shot percentage) .
Most ignore qualitative criteria such as weather, participation (or lack due to injuries or "throw-away" games) and individual efforts.
Goals of some rating systems differ from one another.
Rating systems cannot ignore "throw-away" games. These are games where teams have already earned a post-season bid and have secured their playoff seeding before the end of the regular season, and want to rest/protect their starters by benching them for those remaining regular season games. This usually results in unpredictable outcomes, but without a mechanism to ignore such games (which runs counter to the goals of such systems), this will unintentionally skew the outcomes of rating systems.