Er, you can play provisional balls in competitions, if there is a chance that your original ball is lost or out of bounds!^^^ We know from the extensive commentary here and the heat generated by the discussions about slow play - that perhaps, between sensible golfers (all whom are of course, gentlemen and ladies) playing a provisional ball is, occasionally, the sensible just-in-case option to avoid delaying play by having to return to the Tee; even when the Rules require it (exc competitions).
