Why (if anything) is a planet clearing its neighborhood important?

[halfeye]

Is there a particular body fitting these criteria that you would like to discuss? Or are you just interested in the "what if" game (as I call it)?

I'm interested in the What If. I don't know of a particular case but given the number of extra-solar objects detected thus far, it seems probable that one such actually exists somewhere. So, would it be a planet?