Get to Know the Candidates
First, primary election campaigns are the main way voters get to know about all the candidates. After the national conventions, voters hear mainly about the platforms of exactly two candidates -- one Republican and one Democrat. During the primaries, however, voters get to hear from several Republican and Democratic candidates, plus the candidates of third parties. As media coverage focuses on the voters of each state during primary season, all the candidates are more likely to get some coverage. The primaries provide a nationwide stage for the free and open exchange of all ideas and opinions -- the foundation of the American form of participatory democracy.
Secondly, the primaries play a key role in shaping the final platforms of the major candidates in the November election. Let's say a weaker candidate drops out of the race during the final weeks of the primaries. If that candidate succeeded in wining a substantial number of votes during the primaries, there is a very good chance that some aspects of his or her platform will be adopted by the party's chosen presidential candidate.
Finally, and perhaps most importantly, the primary elections provide yet another avenue though which Americans can to take part in the process of choosing our own leaders. The interest generated by the presidential primaries moves many first-time voters to register and go to the polls.
While some states have dropped their presidential primary elections due to cost or other factors, the primaries continue to be a vital and important part of America's democratic process.