The swing vote is often closely studied when there are elections because it often decides who wins the election. In many elections parties try to convince the swing voters and the people who vote for the first time to vote for them. In contrast to the swing voters, there are other voters who have always voted for the same party in the past. A campaign for a vote therefore often focuses less on keeping the people who will always vote for their party; the parties spend more effort and money on convincing new people to vote for them.
Swing vote Facts for Kids. Kiddle Encyclopedia.