I sometimes use it in town because modern automatics want to upshift very aggresively to maximize fuel economy. That means the engine is almost lugging most of the time, which isn't really good for it. So I'll use the manual mode to keep the car in a gear that results in a slightly higher engine RPM.

It's not like a real manual though, there's no tactile feedback to changing gears or knowing what gear you're in by the position of the shifter, so I don't use it all the time.