Using PowerShell, how do I add an App to a site from the App Catalog?

I have an on-premises SharePoint 2013 farm with a configured and working App Catalog. I'm trying to script site deployment and configuration using PowerShell. How do I add and trust an app to the site using PowerShell?

I can do so using Import-SPAppPackage and Import-SPApp but Import-SPAppPackage requires the path to the *.app file.  This seems unnecessary as the *.app file has already been uploaded to the App Catalog.  The site provisioning script shouldn't need access to the *.app files to add an app from the catalog.  Is this creating a duplicate to the app in the App Catalog?