Why? Because RLAs strategically allocate resources while providing strong evidence about contest outcomes.
RLAs avoid checking too many ballots unnecessarily. Unlike audits that check a fixed percentage of all ballots, risk-limiting audits base the number of ballots selected for audit on the specifics of the contest. Contests with a wide margin can be audited with very few ballots, freeing up resources for auditing closer contests. Even in close contests, risk-limiting audits can often provide confidence in correct outcomes with a modest amount of effort.
RLAs are statistically sound. The American Statistical Association endorses and recommends risk-limiting audits. By using truly random samples of ballots, these audits are able to give solid evidence about the entire outcome of a contest from a relatively small number of ballots. When the procedures of a risk-limiting audit are followed, there is only a limited chance that an incorrectly reported outcome could go undetected and uncorrected.
RLAs are flexible. There are different types of risk-limiting audits, all of which provide statistical accuracy and efficiency. RLAs can adapt to various kinds of voting systems, provided there are voter-verified ballots to audit. The level of assurance given by the audit is also flexible. When greater assurance is needed, more ballots can be checked.