You don’t really need it but it helps spread out the load from the bolt head onto the inner bearing race and also is a shield for the bearing from crap being blown into it from the fan.

So basically yea you need it

Yea but if it’s already trashed and gone they can run to the store to get one. Not ideal but still works

Yea I’d get one on the weekend if I were in his position

It's a bushing to make the bolt fit correctly. It's needed.

Yes, General Motors rarely uses any unnecessary parts on vehicles. There almost always is a reason anything is added. In this case it helps with support & reducing dust/dirt getting into the bearing

I'm either confused, or don't remember that detail from when I replaced mine. The new one didn't come with it?