Picture a crankbait's path as an inverted arc from the time it splashes down to the time it reaches your rod tip. Once the lure hits the water and you start cranking, it has the potential to dive to a certain depth and maintain a generally horizontal trajectory until it nears its point of origin and is forced upward toward the rod. On short casts, the crankbait might not even reach its potential maximum descent, which might not be a bad thing under some circumstances. But when fishing ledges where bass might be posted over a wide range of structure at the same depth, you want the lure to cover as much of that fish-holding territory as possible. You cast as far as you can, knowing that the farther the line goes out, the longer the lure stays at a productive diving depth.