I always use a mono or flouro leader for abraision resistance, especially when trolling and bouncing my lures off bottom.
Too many times I have had clients not use a leader and all of a sudden when trolling the line will break right in front of the lure where it has been banging off bottom.
It's a good thing T60 Flatfish float!!!!
Oh, and for knots, Palomar, Uni and Back to Back Uni.