Expect can help you to automate interactive console applications. For example, expect script can go to some Linux host via SSH with password authentication, make additional authentication procedures (su, sudo) to elevate privileges and execute some commands. Like Vulnerability and Compliance management products do during the active Linux scanning, right? 🙂 For example you can get the list of installed packages and make Vulnerability Assessment without Vulnerability Scanner.
Actually, the tool is pretty old. It was presented more than 20 years ago! And perhaps now it makes more sense to use python scripts, for example paramiko with paramiko-expect. Or even use some software provisioning tool, like Ansible. But my fun was in creating (generating?) a small old-school scripts that could be sent to any remote host (with expect installed) to gather information from the accessible hosts.