There are a lot of different standards and methods for primary elections. Some require 51% and some don't.

Now imagine a scenario were 30% want one candidate (green) and 30% want another candidate (blue).

Now imagine that most of these all agree on their second choice candidate (red).

If 60% of voters agree on red, without RCV, either green or blue will win by a slim margin.

With RCV, red wins.

People complain that they don't vote because they don't like either of the two "front runner" candidates.

RCV gives them a chance to vote for the person they really agree with, while still insuring that their vote won't indirectly contribute to a win for the candidate they hate the most (3rd party "spoiler").

It's a fail-safe that better reflects the true will of the electorate.

It gives people a chance to vote for something they want, instead of simply voting against someone they hate.

AND IT DOESN'T NULLIFY YOUR VOTE.