BW I always predraft, a good friend who spins recommended it. It does help to stop the fibre breaking for me. I can't predict at all what the yarn will come out like especially as I ply the 2 threads as they come. Another friend has recommended that for a more predictable yarn I spin all the fibre the same way and also if you navajo ply that keeps the colours as they are on the bobbin I think.
I also found out that if you split the fibre in half before spinning that ensures you will have 2 bobbins holding more or less the same, I didn't at first:)