According to ahrefs.com 6 of the top 20 pages of the Moz.com blog are category pages, 2 of the top 20 searchengineland.com URLs are category pages and while 0 of the top 20 searchenginejournal.com URLs are category pages, they do have several listed in their top 100.
This data suggests keeping the category and taxonomy pages in your sitemap and indexing them may be more beneficial than has previously been suggested.
Unless you have specific reasons to exclude your category pages, I would suggest adding them to your XML Sitemap and allowing them to be crawled and indexed by search engines. You may be pleasantly surprised by the performance of some of these pages.
That being said, you should do your own research in your industry to make sure that is the best decision for your business and website.
The data here came from ahrefs.com.
Yes, if those pages are useful to users and may find them valuable unless you have specific reason not to. Excessive numbers of category pages or pages little content may not be valuable. Do your homework and think about the searchers intent.
Absolutely not! You MUST do your own research to find what would work best for your web properties in your industry.
Would love to get your feedback on this topic. Do you include your category and taxonomy pages in search results? Why or why not?