Why is uArm shield and FTDI drivers required?

Generally, Arduino boards do not need a driver/shield to drive the servos. Shields are used to drive stepper and DC motors. What is the reason for using the shield ?
Arduino UNO board does not require FTDI drivers to be installed because they use a different communication IC.[Source: How to Install FTDI Drivers - SparkFun Learn]
Why is it required to install FTDI drivers on the UNO board ?

because arduino just give out the angle by pwm signal, the power of the servo is provided by the AC adapter.

Thanks Lily! If you could clarify the need to install the FTDI drivers on UNO, it would be great! I know FTDI has something to do with serial communication.

you no longer have to install ftdi drivers if you have a arduino board with a 8u2 or 16u2 comm chip on the arduino board

Thank you for the quick response Nick !

also the shield just provides an external power source for the servos.