Here's another big reason why I don't pre-tie leaders.
I fish the Canal. Even as long as I've fished, and how well I know the place, I still hang up. When I do, being that I fish 40# mono leaders on 65# braid, I usually break the leader before the braid. I tie off my braid to a barrel swivel with a palomar knot. If I want to use a pre-made leader with a barrel on the end, that means I'd have to use a huge loop in my braid palomar, and thread a 36" mono leader thru it before I tighten down the knot--which is a real pain in the arse to do.
I suppose I could pre-tie leaders with just a Breakaway clip on one end and leave the other end loose so I could knot it to the barrel with an improved clinch. But why bother? It's just as easy for me to tie two quick improved clinch knots as it is to tie one. And it takes more time just to unravel a coiled pre-made leader than it does to tie two clinch knots.
And no--my clinch knots don't fail, even when I tie them in heavy mono
