What functions do political parties perform?
Ideally, parties provide the organization by which an election campaign is run, by which a candidate is presented to the voters, and by which the candidates are helped to garner votes. Ideally, parties represent a particular political philosophy, and that philosophy is presented to the voters and if enough voters agree with that philosophy, its party wins. Unfortunately, in a two-party system, both aim at some amorphous “middle” and don’t really stand for much by way of a consistent philosophy. The best system, one that truly provides voters with a means to demonstrate their beliefs, is a four- or five-party system. Also ideally, voters are given something like Instant Runoff Voting, so they are able to escape from the nonsense of “well, I’d like to vote for X, but only A or B has a chance to win.