I think there's a world of difference between a character using idioms in dialogue--which builds the world, and reflects the way people really talk--and you, the writer, using cliché in the narration. Which is to say:"Bloody hell," said Patrick. "It's raining cats and bloody dogs out there!"
is fine, and characterful, and gets the idea across, butPatrick looked out the cottage window. It was raining cats and dogs across the moors...
is less fine. There's an argument to be made for a tight POV being like dialogue anyway--indeed, I'd make that argument
--but as a general rule of thumb I see the latter done more poorly in slush, and it often comes across as amateurish.
Idioms that get across world building are a useful tool and don't sound the same cliché alarms (he says, using a cliché
):Patrick looked out the cottage window. It was pouring rain like tears falling from the face of Great Bannog...
My two pence :)