All lines and leaders spray water droplets when false casting. Braided and furled leaders a bit more as there is more surface area to hold water. It depends on the light angle as to how much you see this when casting but a surface feeding fish can see the anomaly even if you don't. As Dillon indicated, this observation trains you to false cast away from your quarry while drying and measuring your line/leader...do this regardless of leader type as not only spray but reflected light off your line is a potential alarm as well.
The spliced braided loop on the braid or the sorb loop on the furl is slim and snug when mated to the welded loop of current fly lines and assuming proper mass matching (the Parabolic Test) create little disturbance in the cast or presentation. Yes, for the less compressed .021 monofilament butt, a multi-turn (I like 12 turns) Nail Knot is surely preferable but this is generally tied at home or in camp, rarely out on the river. the slender brass tube of a fly tying bobbin is as good a Nail Knot tool as there is.
Inserting the angle cut tip of a fly line into the loop-cut-off butt end of a Braid, inserting the line 1/2 to 3/4" and applying high viscosity Zap-A-Gap cyanoacrylate makes as smooth a line leader connection as there is. It is important to use this glue not regular super glues as one wants to avoid wicking into the hollow braid. After carefully applying the Zap, wick excess off onto scrap paper and allow to fully cure, at least an hour. At the terminus of the Braid I don't use the loop but, as Dillon wrote, make a 12 turn Nail Knot of O - 1X Nylon and build down conventionally from there to a 5' tippet section.
Such a leader does require some craft and maintenance on behalf of the angler...fine with us as it produces the ultimate in dry fly leader performance. Oh, and yes, I use some all Nylon Cutthroat Furls too, built down the same way from the tip end, never with a tippet ring (ich!). These are a little more aggressive and Ifavor tehm on my 6-weight and the Braid on #'s 4 & 5. These, of course, are dry fly leaders and more or less superfluous for sub surface methodologies.
