A few days ago, I heard a "rattling" sound under my car when I turned it on and when I was idling. So, I brought it to my mechanic and he told me that my heat shield was rotted and it had come loose, so they took it off and that should fix the problem of the rattling noise, which it did.
From what he said, I'm assuming that a heat shield isn't a necessity to have on my car. Does anyone know what a heat shield is and what it does? and if it's optional, what are the benefits to having one over not having one?

 

I don't know which heat shield was removed but they're all necessary. It's just a piece of sheet metal that lives between the exhaust and the car body as well as the gas tank. They also protect fuel and brake lines in some areas. Your mechanic solved the rattle but introduced another potential problem: a lot of heat going into the wrong places.

 

Do you know what potential problems that not having it on the car can cause? In your opinion, would my car be safe/okay to drive for the time being until I have time to get back to my mechanic and ask him to replace the heat shield?
I was also unaware that there are more than one. I have a 2003 hardtop, standard. Do all coopers have the same number of this part and where are they usually located?

 

You're probably good to go for a while. Look under your car and you'll about 3 heat shields running along the path of the exhaust all the way to the tips. Look in the engine compartment in the back and you'll see another one attached to the manifold. Things are especially hot at the manifold and the initial portions of the exhaust going back to the catalytic converter which gets HOT.

 

Think of it this way,there are a lot of people with failing steering pumps because primarily the heat,even with heat shields in place!

So with out the heat shields I believe your just asking for trouble in these summer days,now if your not driving like the proper crazed spirited mini driver most us tend to be and just being easy on the gas trying to keep the car at a cooler running temp it shouldn't be to bad depending on where the heat shield was located

Personal opinion,I would have to Drive it and just replace heat shield just as soon as I could..
As don't have another ride...