Actuators become truly useful when they are controlled by a microcontroller (like Arduino or Raspberry Pi Pico) and respond to real-time inputs from sensors or switches.
For example:

• Pressing a button could make a servo motor rotate.

• A light sensor could turn on a fan when it gets too bright.

• A motion sensor could trigger a door to open.

This interaction between input devices (sensors/switches) and output devices (actuators) is what makes a system smart.