Approval voting allows voters to approve or disapprove of each candidate on their ballot individually, and the candidate with the most approvals (votes) wins. Approval ballots look just like plurality ballots except the instructions at the top say "Choose one or more."
1. Identify the front-runners in the race (candidates most likely to win).
2. Of these front-runners, vote for your preferred candidate.
3. Also vote for any other candidates that you like better than your preferred front-runner (if any).
Avoids Vote Splitting/Spoiler Effect
Since you can give equal support to any number of candidates, your support for your favorite can never hurt your supported lesser-of-two-evils candidate unless your favorite actually wins, which you would prefer anyway.
The importance of this attribute cannot be overstated and really ties into many other benefits. A simple method means lower cost, greater transparency, better security, easier voter education, faster tabulation, and greater voter trust. A switch from plurality to approval only requires changing the instructions at the top from "choose only one" to "choose one or more".
With so much recent controversy over voting security, the last thing we need is a significantly more complex voting system with a dozen rounds and come-from-behind winners. Approval tabulation and reporting is just as simple as with plurality.
With voting by mail becoming increasingly common, ballot length is important. Switching to a voting system with ballots that are five times the length could either double the cost of the election or prevent the use of vote by mail altogether.
Approval ballots can be tallied at the precinct level and then simple totals are reported. With systems like RCV, every single ballot must be transmitted to a central location where they are all counted, and only then can the runoff rounds to determine a winner begin. This transportation and centralization introduces new security concerns.
Since there is no vote splitting, a single Approval election can be held, saving the money of holding primaries or runoff elections.
Voter Satisfaction: Research has shown that Approval voting has significantly higher voter satisfaction than all other methods except STAR.
While research shows STAR voting to have the best overall outcomes, Approval is the 95% solution, having much better outcomes RCV without any of the cost or complexity.
While Approval is more expressive than plurality, it does not allow voters to express a preference between candidates that they support. RCV is arguably more expressive than approval, and STAR is the most expressive.