Why do I need to buy touch sensor in my project?

Hello

This question may looks dumb but I made a capacitive sensor on my Arduino with this library (http://playground.arduino.cc/Main/Capac ... n.CapSense) and it worked pretty well.
Almost every tutorial and product sold to make touch project are using a MPR121 chip. Why should I buy a touch shield / MPR121 chip if I can just use a resistor between 2 pins?

A shield is more reliable, small/compact, and takes up less I/O pins to measure capacitances for more numerous objects.

It all comes down to how you want to design your project and what your requirements/constraints are.