I'm thinking of adding a noindex tag to all the ads pages (millions of them) since they bring no value in terms of organic traffic but waste over 90% of our crawl budget. Plus, most of them end up as crawled but not indexed in Search Console.
The logic says that they shouldn't be sent for crawling and indexing but the logic doesn't always work in SEO. I wouldn't want the bots to check so many of my ads every day but to concentrate on the category pages which are the ones bringing the most organic traffic. Do you think it's worth a try?