WhatIf instructs the command not to make any changes, but merely to log what it would do. You can "Remove-Item C:\Windows -Force -WhatIf" and it will output "What if: Performing the operation "Remove Directory" on target "C:\windows"" but not delete anything.
(implementing support for "whatif" is optional, so you can't casually use it on any given cmdlet without first checking that cmdlet supports it and makes sensible use of the parameter instead of ignoring it, but the idea is there).
(That's the common Unix shell name for it, though it's not entirely consistent -- which is another problem with using Unix built-ins!)
One thing I've noticed is that it's really frustrating (and not at all helpful) to require perfect validity from a shell-like tool. There's just too many times where you want to edit something into something else, without needing to find a perfect path of valid and meaningful syntax at every intermediate step. So if you have a flag on an operation that doesn't understand that flag, the flag will have a (?) badge to indicate that it won't be understood or used, but the pipeline will still run.
Strukt doesn't do 'rm' yet (and nobody has ever requested it), but it does have other operations that do writeback. Once you add one, automatic updates are disabled, and you have to explicitly run the pipeline each time you want it run.
We really need a new cross-platform low-level framework for lego-like operations, like shell commands but updated for the 21st century.