I don't know what you're getting at there. Sure, if you call an empty function, nothing happens, but that doesn't mean other non empty functions won't also be called:
won't prevent foo from being called when a <li> is hovered. On a hover, it will call foo, and then it will call the empty function, which doesn't make much sense.
And how does the fact that jQuery and CSS are different things have anything to do with anything?