Not just single issue - you can vote the party or candidate that "far, far from the typical public position on most things but preferred by me", without opening the door to the ones you actively oppose.

I would likely be a green party voter by choice, but when there's a republican on the ballot, there's no way I'm voting green - the downside of having the republican win is (for me) larger than the downside of not casting my vote according to my conscience.Adjust to suit your own political preferences - perhaps you'd like to vote libertarian but are worried about allowing the crypto-DSA democrat into office, etc, etc.

This is MAJOR. The US, the UK and other first-past-the-post systems need RCV or something similar so badly.

[EDIT: yes, STAR is likely even better]