Let's say I'm upgrading a large software enterprise application. I start the upgrade process. After 5 minutes, the process determines that the upgrade will require an extra 1.5GB of storage and asks me if I would like to continue with the upgrade. After 15 minutes, I'm presented with a username / password prompt to enter credentials to retrieve a package from an external resource needed for the upgrade. After another 5 minutes, the upgrade process has detected that there are a number of derelict files detected and asks for permission to remove these files.