The Kill Sloop command shuts down the Sloop Sail entirely. Once you execute this command, you will not be able to use the Sloop or set preferences until you restart your computer.
This command is not undoable.
The Kill Sloop command is primarily intended as an easy way to uninstall and delete or replace the Sloop Sail.
If you simply want to disable the Sloop, but don't want to delete it or install a newer version, you should use the Sloop Off radio button in the main preferences dialog instead.
The reason this command exists is that even when the Sloop Sail is off, it is still technically running, even though it doesn't use any processor time. Because it's still technically running, if you drag the Sail to the trash and try to delete it, the Finder won't let you.
The Kill Sloop command completely stops the Sail so that it's no longer running. Once it's killed, you can delete it from the Finder.
(Note: Even though it isn't undoable, if you kill the Sail by accident, you can also quit and then restart the Rudder. The Rudder will then attempt to reinstall the Sail.)