Archiving your app allows you to get rid of apps that you no longer need. When you archive an app, you will not see it in your list of apps in the Blocks Editor. You will also not see it in your list of apps when importing Blocks apps to a site. You will no longer be able to edit it in Blocks, or install it on any site.
No unarchive Note that once you archived an app, you cannot unarchive it.
If you archived an app that is already installed on a site, it will continue to appear and function in the site. The site behavior will not be broken. However, you will not be able to maintain the app that is installed. If you hover over the app in the Wix Blocks > My Apps menu, you'll see that you cannot open it in Blocks to edit it.