What good does nike+ sensor do with ipod nano? Already works fine w/out

Hello,
I have the small square ipod nono (or touch)..can't recall...think it's the 4th gen square one.
I like the Nike plus feature that it comes with.

Everything I read says that it needs a Nike + sensor in the shoes or somewhere for it to work.
But I don't have the Nike+ sensor on anything and it seems to work just fine with simply the Nike+ app on the ipod.
It tracks my steps and distance and calories without any sensor...

My iphone has a sync feature that will sync it to the shoes but the ipod does not have anything in the app that seems will sync with the shoes and if it works fine on it's own, what is the point of having the sensor. I don't quite get it.
Anyone have any experience with this?
Just wondering if I should purchase a shoe with Nike+ or the sensor or just disregard it and use it as is...which seems to be fine now.
thanks,
M

Since the 6th gen Nano the functionality of the sensor (as you note) has been built in. So there's no need to get the separate sensor.

thanks for clearing it up!!