The article gives a few examples of concrete things you can do:
- Build, run, and publish containers
- Containerize language-specific builds
- Run integration tests in ephemeral environments, in a repeatable way
- Run your tools in controlled sandboxes with only the files, secrets and network access they need
It also mentions what you might replace with it:
> When a workflow is too complex to fit in a regular shell, the next available option is often a brittle monolith: not as simple as a shell script, not as robust as full-blown software. The Dagger Shell aspires to help you replace that monolith with a collection of simple modules, composed with standard interfaces.