I can't imagine broadcasting my current location to the world. There are so many risks that I don't even know where to begin. If you like this feature, good luck and godspeed. Hopefully you don't get robbed, stalked, or worse.
And don't think you're safe just because you think that you have your account set to only allow friends! People's accounts get hijacked all the time letting some other stranger in. Also, your friends may have people in their family or others in their house with access to their computer and thus the things that are posted to your wall. What if a computer gets lost or stolen? What if the people you added aren't who they say they are or if you don't know your real friends as well as you thought you did and they decide to do something with the knowledge that you'll be away from your home or off in a secluded area?
The point is that no matter how unlikely you think those things are, you suffer risks from people knowing your location that you don't otherwise. Even if you don't want to be as risk avoidant as me, the last thing you want is for there to be a way for your location to be broadcast without your consent (which of course is the default option in Facebook).
Even if you feel ok posting where you are sometimes, you don't want it to be automatic or something other people can set for you so turn it off!