How much is a locked cage really needed?

To me the risks are really someone messing with your cables and taking you off line, or accidentally pulling a power plug, which is QOS really. Not security. Can't remember when I heard of someone carting off a server or plugging in a cable to the console port (once they have gotten even into the racks and are on cameras) and doing any harm. Even if this does happen it seems fairly remote and not a concern unless you are really doing something so important that you need to lock up the servers. Sure price not being an object why not lock them up.