It buys you sophisticated systems for filtering duplicates out of results.
If you serve the same content via multiple URLs, search engines will choose which one to display in results. Sometimes, this results in a choice that webmasters don't like - particularly if search engines don't consolidate things like link popularity to a single URL. So, a site owner can end up with several weak URLs instead of one strong one - so-called duplicate content problems.
Search engines don't really care - it's very rare to see duplicate content in a single result set these days. This option (as our redirects) are a way for you to choose a preferred URL, as opposed to letting search engines do it for you - sometimes to your disadvantage. This isn't you helping them out, but the reverse.
Whether this element actually works or is a good implementation is a different question, but this isn't like nofollow.