This feature, from Pascal's understanding, allows you to upload new versions of your application, start up the new version and refuse sessions for the instances running on the older version.
It is uncertain what will happen if the new version of your application makes changes to your database schema (e.g., uses ERXMigrations). The old instances may raise exceptions before they can gracefully shut down because the schema no longer matches what the old application's EOF expects. Try it out on a test server first and then update this page so everyone knows!
If you call