Whats wrong with doing it in windows? In this day and age its the best option. You go to disk management and partition/format as needed. No need to worry about switches.
I don't remember them that well after using windows for as long as I have. I think the /s switch puts the system files on the disk/drive so that its bootable. (command.com, and perhaps 1 or 2 other files.) The answer to the question assuming I remembered the switch correctly would be if you need it to be bootable then use /S. If its just a data drive don't' bother.
Since we are talking about OS disk, I would say just format the disk using your OS installation disk, they all provide this possibility as part of the installation.
If you want to format just to remove sensitive information before selling the HDD or entire PC, then any option would do, but you can probably find some free low-level and multi-pass formatting software that would really clean it out.
Actually, I think the star isn't even necessary; I remember an old incident when someone wanted to "rm -rf /$DIR", but mistyped "rm -rf /$DRI" ... needless to mention the results as this was executed as root.