Most of the use cases I can think of deal with the iterative process of development, make a change, clean all modules, install all modules etc
Regardless it could serve some usefulness in CI or release management regardless.
So say you wanted to clean all modules, you could do a mvn clean followed by a mvn install in a script or on the command line but what if you could just provided this in one command.
For example mvn clean install,clean deploy where it would actually clean and install all modules, then if that succeeded it would then clean and deploy all projects. Obviously there are some semantics that are unclear like if the second deploy could reuse the previous builds outputs (if clean wasn't done) etc.
Unfortunately I can see that the syntax might be confusing and consideration to how it would be escaped on different consoles/platforms might be troublesome. It might be just that we should stick to scripted process with separate executions of the maven binary if we really need this functionality.