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