This idea is about having the possibility to create an (optional) dependancy between specified servers, so that a server will not be updated until the server it depends on is already considered fully up to date.
This would be extremely effective -for instance- for Applications that require the Database Server to be up and running before the Application Server. Especially in large environments these are challenges that SCCM currently doesn't provide any solution for bar scheduling Application Servers in a seperate, later window (which is not ideal for multiple reasons).