Do you want to build a robot using lots of servo motors like a hexapod? Run out of PWM outputs on your micro or using a Raspberry Pi? Maybe you just want to control LEDs with 12-bits of PWM brightness levels? Then this is the module you have been looking for!
The Arduino Motor Shield uses L293D motor drivers and a 74HC595 shift register to drive 2 servo motors and 2 stepper motors or up to 8 half-bridge drivers.