Advanced metrics can tell us a lot about a player, and can act as more predictive instruments than traditional stats to give clues as to how a player may produce in the future. If you have a pitcher with a hilariously high BABIP, good strikeout to walk numbers and a high ERA, you can be relatively confident that things the pitcher doesn’t control - balls in play - will normalize over time, the strikeouts and walks will stay roughly constant, and the ERA will fall.
That’s how this works for 99% of players, but there are outliers in every dataset.