It is important to learn how to use the serial port node , even we have the Firmata node because there are many different types of shields, sensors, and other devices that have their own libraries, and use more obscure protocols other that analog/digital read or write.
Additionally, there are many edge sensors and robotics actuators that use UART , ISP or I2C communication.
The good thing about Arduino is that there is a library for almost everything, making it easy to use as a mild form of C++. Knowing how to send and receive data through the serial port allows you to take full advantage of all the libraries and communitty examples .
Additionally, if you plan on working with stepper motors, DC motors with encoders or brushless DC motors, it is recommended to use Phidgets. They are easy to wire and have proven to be precise and safe. Additionally, there is a NuGet package available to use with Phidgets, which eliminates the need to use Arduino or C++ coding for serial communication.