While there may not ever be a "perfect" lens, there has long been a need for a one-lens solution for shooters who want to head out the door with one camera and one lens over their shoulder. The reasons vary. For some it's a matter of convenience. For some, it's a matter of pure laziness and for others it's the fear of getting dust on the sensor. For frequent flyers it's a matter of logistics, i.e., there's a limit to how much airlines allow you to carry aboard the plane (almost all of these lenses are surprisingly compact).