Iced Coffee and Metal Spoons

I have been making iced coffee since I was a teenager. I learned from my mom. I have always put a metal spoon in the glass, along with the ice, as she did. She told me to always do this, because the spoon absorbs the heat from the coffee and prevents the glass from cracking.

Is this really true? I mean, it sounds like it should be true: metal is a good conductor of heat, and so takes the heat away from the coffee and the glass. Or did she just make it up somewhere along the way, and I have always done it that way because she does it that way?