Chimes, blinker sound, Onstar sound and steering wheel controls are the benefits of getting special harness(es). If you don't care about any of that, then you should be fine with just splicing it into the existing radio harness.

Edit: Just remember that your "lights on" warning chime won't work either. I drained my battery twice since I disconnected all annoying chimes lol

 

I would recommend the steering wheel harness if you have the controls on your car. I thought I needed the other expensive harness that makes the sounds but you dont need it really save some money.

 

I think all the newer GM cars have the warning chimes now thru the radios? seems odd

 

My chimes dont come from the radio. They come through the speakers but they all still worked with the radio out of my car. I have 2006 cobalt so maybe it just depends on the year.

 

Yours has the chimes speaker built into the instrument cluster.

 

much better set up imo lol