Matrix keypad is widely used in our daily life. Often, a matrix keypad is available in 3×4 or 4×4. For your information, the matrix keypad is a good substitution to normal push button. Matrix keypad offers more input to the microcontroller with lesser I/O pins required as compared to buttons. Consider your system needs 16 inputs, you require only 8 I/O pins with a keypad instead of 16 I/O pins. So you can actually use the extra 8 pins for other functions.