Far greater control over the car, they're more efficient and they're simpler and cheaper. Honestly, if you're someone used to driving a manual, switching to an automatic is uncomfortable. The car doesn't feel entirely under your control. The clutch allows so much more than just switching gears, it allows you to vary the output of power and provides so much feedback as to what your car is actually doing. My dad's got an automatic SLK and it's frankly weird driving it. That feeling of lack of control is unnerving.