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 I/O pins required as compared to buttons. Consider your system needs 16 inputs, you requires only 8 I/O pins with keypad instead of 16 I/O pins. So you can actually use the extra 8 pins for other functions.