That is correct, that is how you run it.
Just realised that the parameters can be a bit confusing.
In summary:
Remove-OrphanedData -Datastore ds1
will show orphaned VMDK on datastore named ds1.
When you add the Delete switch, the function will delete the files it finds.
Remove-OrphanedData -Datastore ds1 -Delete
It is safer to first run such a delete with the WhatIf switch.
Then the function will show which files it would delete, but not actually delete them.
Remove-OrphanedData -Datastore ds1 -Delete -WhatIf
This is in fact producing approximately the same output as if you run the function without the Delete and WhatIf switch.
The only difference is that you will get a line that starts with "What if: performing..."
To run the function against all your datastores, you can do
Remove-OrphanedData -Datastore *
I'm planning a v2 of the function that will have some more intelligence as this version.
But don't hold your breath 