If you have worked on deploying packages via apt-get, you are probably familiar with a couple of forms of interruption during the package installation and upgrade process.
The first is the text menu shown during package upgrades that informs you that a new configuration file is available and asks if you want to keep your current one, use the new one from the package maintainer, or show the difference.
The second is the occasional ASCII dialog that interrupts the install/upgrade and ask for essential information before moving forward. The screenshot below is the dialog you get when installing MySQL or MariaDB, asking to set the initial root password for the database.
The problem, in this age of cloud scale, is that you often need completely silent installations and upgrades that can be pushed out via Configuration Management. Even if this is a build for an immutable image, you would prefer a completely automated construction process instead of manual intervention each time you build an image.