Question: In my company, we have had a policy of tagging every release. Someone new joined, and he suggested that instead of formally using a Tag, we could just leave a comment for the release build when it is checked in. I like using a Tag, but, obviously, we can also get to the source code for a build also by looking for the comment. The only advantage I see is that because our product spans multiple technologies, we can group the source code for both in the same directory with a folder for each. **Is there some other advantage of tagging releases that I'm missing?** BTW, we are using SVN.

Answer: 
Some customer who cannot upgrade to a newer version ask you for support for version x.y.z. A tag with that release will help you identify the code you need to inspect. Ask the new guy to search the release using commit comments. Please, do it!
Another reason to use tags instead of revision numbers to track what you released is it's easier to keep links/references to tags than to revisions of trunk (or branches). References to particular paths at some old revision can break if you reorganize your trunk (or branch) folder layout in the future. Tags don't change (by convention), so they don't have that problem.