Multiple versions of an existing template allows you to A/B test templates, track version history, and compare contents between templates.
Here you can create multiple template versions with slightly different content so you can A/B test templates and analyze which template performs best.
You can also see the version date history of your templates so you can determine which templates are up to date. You can view all versions of a template, subject line, created at and updated at dates.
Note: It's not currently possible to edit template versions.