Not sure what you mean by "separate releases", but we copy from the trunk or branch we are making a build of into the tags folder with a descriptive name, like Proj-1.20.33
This way, for each build we have made, we can go back to that specific version. Generally, you would not want to make any real changes in a tag. For us, we go ahead and change some version numbers for the code and installer via our automated build process, so only those changes get merged back, and even then, that is the only thing that would be modifying those particular files.
The SVN Book talks about this a bit in Common Branching Patterns and the Tags entries.
