Any kind of modest weighting on the hook shank adds a "keel effect
" so lures don't roll over, but run straight and true.
Bob LeMay is credited with tying in multiple 1/8- to 3/4-inch strips of wire along, rather than around, the hook shank to create a "keel effect
." He does this with Bendback streamers, and that weighted shank (which is then over-wrapped with either chenille or similar body materials) not only sinks the fly but encourages it to swim in the correct hook-up manner, in the same way that lead eyes are tied under the shank of bonefish flies.