The target of Teardown is best described with the usecase on the Teardown wiki page:
Matt is a laptop user, when he shuts down his laptop he doesn't want to have to wait for almost a minute before the laptop has actually powered off.
What it actually does, is remove all redundant and unnecessary symlinks to init scripts in the rc directories. Most scripts only send a TERM signal to their corresponding processes while this is also done by sendsigs. So most of them are redundant. On the teardown wikipage you can find a list of init scripts the developers found where only sending a TERM signal or doing nothing at all!
To those who are thinking, "What the **** is TERM signal?", Teardown just makes your computer shutdown within a few seconds (read: very fast compared to the current shutdown process).