If you're looking at a marina or anchorage and want to know things like staff attitude, holding, or whether the facility isn't quite up to it's advertising -- this is the best source. You might not want to put 100% faith into every user review/comment, but it's more data points than you can get just by looking at a chart. If there's a recent change or hazard, it's more likely to be there on AC than in a printed cruising guide or chart (and even if you update your charts, AC might have changes before the NOAA updates).