SEO meta tags: "NOINDEX,FOLLOW" not recommended

Happened across an interesting bit in a Google Webmaster Central Office Hours, right around the 38 minute mark in this session. I've paraphrased here for clarity and conciseness:

Q: We set our product category pages as NOINDEX,FOLLOW. Is Google seeing our product URLs in those categories, or are they completely 404 in Google's eyes?

ANSWER: If those products are only linked from pages that are within the set of pages that are marked NOINDEX, then it's going to be hard for Google to understand that those products are actually useful and important.

There is some nuance here. If you link to those products from elsewhere in the site, that helps them get indexed and tell Google they might be important. If the various products interlink to each other, then that's a signal of their importance to each other, and that can help. But if the category page is important to helping real humans understand and find the products, then Google needs to see that help, too.

Tl:DR: When you use "NOINDEX", you are telling Google "Do not use this content to help determine what is important".