Are tag pages useful?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Victor Castillejos: Seriously? I would walk away, he is the typical client that will only give you problems, he doesn`t understand 2 simple things. Who is the expert? Why he is in problems? But this is only my humble opinion
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  Justin Y: I don`t think it`ll cause harm if you just use no-index and remove them from the XML Sitemap. To me tags are only useful for the user experience and not so much in search. I choose to not have my tag pages indexed to help avoid duplicate content issues and duplicate meta data. By excluding them from the Sitemap it should also help with crawling for indexing pages and posts that are more valuable.
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  Sławomir Zdunek: I agree with +Justin Y about using noindex on tags. That`s the way to go. I don`t think this client is absolutely wrong about tags. I guess he heard something about them and wasn`t sure if they give any value. I think using tags without any safety measures as +Justin Y suggested could be the source of duplicate content. As for clients I think very often they need some more information on functioning of websites. Of course the easiest way is to say goodbye to them but not everyone can afford it. Especially at the beginning of your "career" you take everything to make ends meet and later you can start thinking of choosing the clients.
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  Tim Capper: Ditto to all above. I would keep tags as a UX but obviously make them "noindex". If he has more then 2 tags per post I would also clean this up - I think 2 to describe a page is more then enough, any more then this looks messy.