Assume that you are moving towards a complex microcontroller project bundled with blinkers, beepers, and a display panel. To link a standard 16×2 LCD directly with the microcontroller, for instance ...
I2C is a wonderful interface. With four wires and only two GPIOs, you can connect a whole lot of sensors and devices – in parallel, at that! You will see I2C used basically everywhere, in every phone, ...