If you have a process that writes stuff to a file inside a container (not in a volume or mounted path), stopping a container without destroying it doesn't delete the modifications. Starting the container again may allow the process to read the contents of the file, possibly continuing its execution from some checkpoint.
Other use case would be with stateful containers such as running a database, stopping it and starting it again without losing data (which already should be on a mounted volume)
Interested to know if there are other use cases.