What is the big deal with metallic taste in the mouth?

Might be something. Some metallic taste comes from leaking restorations. Some come from two different restorations of different materials which sets up a battery and dissolves chemicals in your mouth. Sometimes it can be related to taste buds in your mouth or neurological problems. Best have it checked out by your dentist.
More history. Usually "dysgeusia" with an odd metallic taste is from taking medications (even calcium carbonate) or "just happens" & is never explained. I trust you are otherwise well & do not have occupational exposure to lead, mercury, or cadmium. Try running floss across your tongue, and using plastic utensils.