Voting in primaries are very low compared to voting in the General Election. Many voters do not see a reason to vote because they mainly focus on the Presidential ballot. Since many voters have decided to vote for the nominee of the party, they do not see a reason to vote. There are many benefits to voting in the primary besides choosing between candidates.
Voting in the primary will allow a voter to become a precinct chair. Precinct chairs are elected positions that require candidates to have voted in the primary. If there is an open seat in between elections, then the voter can be appointed. Another benefit is the party often votes on rules. Those that do not vote cannot let the party know what we really feel. Another benefit is that it is a good test run for the real election. You may discover that you have been taken off the roles, or that you do not have the required ID for voting. The voting polls are also in the same location as they will be during the November election. You can determine that real democrats run in the election. In 2014 it was discovered that a Tea Party Republican was running in the Democratic Primary. The candidate received a large number of votes. If it wasn't for the Party making a big push not to vote for the candidate then it is possible the candidate would have one. Then Democrats would have been astonished to have a candidate that was against President Obama. The optics of every vote. Right now many are complaining that voter turn out is low. Every vote adds to the rolls and shows that democrats are ready to win. Lastly, bragging rights will be yours. It sure is fun to say that you voted not just in the election, but in the primary.