There is the legal side (thanks Islander Jock) to this question about can another A/C be on the runway when you land on it, and then there is the just think about it side. How would you feel when you sit at the end of the RWY cause you didn't have time to back-track because your mate was on finals, and asked if he can land while you sit there....and then his brakes fail, and the only thing between him and the "clearway" is you? I'd be feeling pretty stupid!.