Tagging now lets you profile and categorise customers, contacts, opportunities, problems, quotes, orders, documents...you name it! Once you've set your tags, these can be used to filter lists of companies or contacts (or virtually anything) when reporting, enabling you to efficiently segment your data however you want.
For example, if you're selling sportswear and accessories, you could add tags to indicate customers who are interested in a certain sport, like "Cricket", "Rugby" or "Tennis". From there, you could add those with a tag of "Rugby" into an email campaign when you have an offer on for all your rugby-related products! And, if you use different tags for different things, say several tags for sports, and other tags for other things, you can group all the sports tags as blue, and all the tags related to (say) their premises in green. It's totally up to you. In fact, the beauty of tags is their flexibility!