Something no one has mentioned yet about using SI is that it's good in the flats for finding structure. I'm one of those who prefer DI over 2D because of the clarity of what I'm looking at. As for SI vs DI, a newer body of water or different area of the lake would require SI to locate structure. However, if you're fairly familiar with a particular area, and are adept enough of a Crappie fisherman to know that you should be working drop offs and submerged creek channels, etc, then I find the DI much more useful. Especially if I've heard reports of what depth the fish have been being caught in recently. I'll work the banks at around those depths until I find structure and fish. To me, both SI and DI have become an important tool in locating structure, but when fishing my favorite waters, SI is rarely used.