even though 60% of the voters prefer either candidate A1 or A2.
Cardinal voting methods are immune to vote splitting, since each candidate is rated independently of each other. Pairwise-counting Condorcet methods minimize vote splitting effects. Plurality-runoff voting methods (like Exhaustive ballot, Two-round system/Top-two primary, Instant-runoff voting, Supplementary vote, and Contingent vote) still suffer from vote-splitting in each round, but can somewhat reduce its effects compared to single-round plurality voting.
A well-known effect of vote splitting is the spoiler effect, in which a popular candidate loses an election by a small margin because a less-popular similar candidate attracts votes away from the popular candidate, allowing a dissimilar candidate to win. As a result, the notion of vote splitting is controversial because it can discourage third party candidates.
Strategic nomination takes advantage of vote splitting to defeat a popular candidate by supporting another similar candidate.
Vote splitting is one possible cause for an electoral system failing the independence of clones or independence of irrelevant alternatives fairness criteria.