Yeah, clippy will yell at you if you use a match with a single arm - I personally don't hate matches with a single arm, but I'd rather not fight clippy (ie. come up with my own clippy config, enforce it onto every project I maintain etc.)
I've hit this warning a few times where I expect to add additional match arms to be added in the future, always bugs me that clippy in that case steers you towards some change you know you'll end up undoing.
This is what #[allow(clippy::whatever)] is for.
That's why they're warnings, not errors. I don't really understand the inability of some people to ignore warnings while they're working.