Auto-Archive can be a powerful feature to save money as it can enforce that an asset will only be billed once in the live/online price-tier and transitioned to archive automatically after that.
Auto-Archive can be activated on a per-file basis during the upload of a new file:
Direct-to-Archive
In this dialogue you can choose if the uploaded asset should skip the live storage and go right into the archive-tier. Read more about Direct-to-Archive.
You can also choose to activate Auto-Archive on a global level in the settings. Either as the new default during upload (this can be overriden by the uploader), or by enforcing the setting (cannot be changed by the uploader).