International Lancia Forums

I had a strange experience with my Thesis for a few days ago. It's a 2,4 jtd 2003. The belt pulley wheel fell off from the crankshaft. The rubber between was broken. But my question is: for what is that pulley? Everything is still working fine. AC, charging, power steering etc. the belt is still in in it's place too. Is it only for vibration damping? Because it's no belts connected to it in my car...
Please advice. Thank you!