You know, the one that outputs this=>
------ Clean started: Project: Foo.Bar, Configuration: Debug Any CPU ------
========== Clean: 1 succeeded, 0 failed, 0 skipped ==========
What it is cleaning?
The output directories - it removes the code that it's previously built.
It doesn't remove the bin/obj directories themselves (or the Debug/Release directories beneath them), just the actual .exe, .dll, etc files. Unfortunately this makes it less useful for my usual use of cleaning up output directories: when I want to zip up the source code. As the Clean action doesn't do this, I usually just delete the bin and obj directories directly.