Motor Control Shield - L293D contains two L293D motor drivers and one 74HC595 shift register. The shift register expands 3 pins of the Arduino to 8 pins to control the direction for the motor drivers. The output enable of the L293D is directly connected to PWM outputs of the Arduino.
To increase the maximum current, the L293D allows extra chips with "piggyback". Piggyback is soldering one or two or three extra L293D drivers on top of the L293D drivers on the board to increase the maximum current. L293D allows parallel operation.
Motor Control Shield - L293D is able to drive 2 servo motors. The servo motors use the +5V of the Arduino board. The voltage regulator on the Arduino board could get hot. To avoid this, the newer motor Shields have connection points for a seperate +5V for the servo motors.