For animation in production, how do people know "Ok, these images are clean enough for final render"?

Also, is some kind of denoiser used in comp for cleaning up noise in animation? If so, how often and what denoisers are usually used?

Thank you.

I'm not experienced in animation/production work - but likely experience is the number one factor; and I would suspect a number of test renders at key points which only cover a short range of the animation but if 'succesful' in giving the results desired is indicative of other areas being the same that have similar content processed.