If you have content, you tag it. If you have web content, you tag it in your content management system. Your authors do it every day. And it feels somehow free. You never get a bill for content tagging–people who already work at your place spend a few minutes doing it every day. So why would I need to automate content tagging?
For some kinds of content tagging, manual tagging is fine. It’s perfectly OK for you to ask authors to decide which content format their page is–they should know if they are creating a product spec or a white paper or a case study. But if you ask them to tag a document with the right industry or the right subject? Good luck.