Draft grades dont say something about the upcoming year but they can be a good predictor of a teams performance in upcoming years. A good score means strong young players on the bench and good depth in years to come. A low score might mean trouble is on the horizon.
The draft grades determine which teams get to pick their drafts and in which order. Usually, the teams that are not performing as well, get to choose first. There are also trades that can happen within the process of drafting a player. A team with a lower grade can trade their place for a deal with a better team who would like to pick a player earlier on.
The NFL draft grades are meaningful. The NFL would not have such a tool if there wasn't a use for it. In addition, it keeps teams, players, coaches, and owners interested. It also gives the viewing audience something to think about. Football season might be a ways away, but things like the grades keep people tuning in for information.
I believe they mean a lot to the fans and the opposing teams strategy. If a rival team gets an A+ Draft grade, you might be a little more afraid and watch that team more closely in spring training and in pre-season. If your teams gets a good draft grade, the fans might be more willing to support the team, buy tickets and merchandise and get behind the team before the season starts. If the team gets a bad draft grade, the fans might be less willing to support and spend money if the team doesn't get a good draft grade.
Experts can only guess how good draftees will do in the future. These players are all under 23. How can you grade now how they will do in the future? They can only grade what those players have done in college, which can become completely different than their professional career in the NFL. Draft grades do not mean much of anything.