If I'm nymphing, I like a split shot about 16" up from the fly. An un-weighted fly I would think presents itself in a more natural way, and I've done very well using this method. If the stream is high and fast I'll use a tungsten bead fly to keep it down near the bottom. Some beads of course represent an air bubble, are non-tungsten, and almost weightless in themselves. I use some beads to imply a head on the insect I'm trying to represent. Point being it's all good and streams and their conditions require varied fly's and presentations. And that's all I have to say about that.