Microcontrollers are digital and they have only two 'power' states, on and off. This makes them very suitable to control relays. Also it is possible to supply a varying power from a microcontroller. It operates at very high frequency in MHz and with Pulse width modulation (PWM) is provided the ability to 'simulate' varying levels of power by oscillating the output from the microcontroller.
Microcontrollers are widely used due to their benefits. They can be programmed for different applications. The program is written based on the specific requirements for each project. When necessary the program can be changed without changing the hardware.
Some applications of microcontrollers are in devices for:
Light sensing and controlling
Process control and automation
Temperature sending and controlling
Fire detection and safety devices