Hi Kathy,
Good question. Using the Save As method on an existing project to create a copy is very similar to using templates. I'd say the main benefits to using templates over the Save As method are:
* Templates appear in your templates library in Storyline (Home > New Slide > Templates), so you just click a template when you're ready to use it.
* You can't accidentally mess up a template. Each time you launch the template, Storyline actually creates a new project for you based on the template. The template itself remains unchanged. But with the Save As method, if you forget to Save As first and just start making changes, your "template" file could be compromised.
All in all, you can use either method, but templates simplify the process a bit. I hope that helps. :)