Wikipedia has a really comprehensive article [1] on this type of voting, but for most purposes of discussion this is the relevant paragraph: "Proponents of IRV

Wikipedia has a really comprehensive article [1] on this type of voting, but for most purposes of discussion this is the relevant paragraph: "Proponents of IRV note that by reducing the spoiler effect, IRV makes it safe to vote honestly for marginal parties, and so discourages tactical voting: under a plurality system, voters who sympathize most strongly with a marginal candidate are strongly encouraged to instead vote for a more popular candidate who shares some of the same principles, since that candidate has a much greater chance of being elected and a vote for the marginal candidate will not result the marginal candidate's election." It's generally viewed as a means of gradually stepping away from some of the problems of a two party system. https://en.wikipedia.org/wiki/Instant-runoff_voting https://en.wikipedia.org/wiki/Instant-runoff_voting