I just purchased a new Berkley and Jensen microwave. I would like to know what the metal rack used for? There is no explanation in the owners Manuel.
Some microwaves have racks so you can cook two dishes at once. In fact, you can buy generic racks for this very purpose. However, I also read that some hybrid microwave/convection ovens include metal racks that must be removed if you're using it in microwave mode. You could check with the manufacturer if you want to know for sure. They may recommend removing the rack if you're only cooking one dish at a time.
Contrary to popular belief, metal is not as much no no in a microwave IF AND ONLY IF something else is in the microwave as well.
That metal rack is a grill, it will get hot enough to put grill marks on your food.
Do NOT use it unless you have food in your microwave. Leave it out UNLESS you are using it. And make sure your food hasn't dried out when you are using it.
I have never used mine, I don't cook with a microwave, I merely use it to reheat occasional small bits or to soften butter in an emergency, and the kids use it to heat up leftovers sometimes but I don't cook with a microwave.
I am not sure about your specific make and model of microwave, but I have seen metal racks used in combination microwave/ovens with broiling function to speed up the broiling process as the food will be closer to the heating elements.
This is especially useful on the combined microwave/broil function as these ovens will constantly switch between microwave and broil.