I live in Portland, where we only get ice/snow a few days a year, and studded tires are cheap insurance for me. $120 for a pair of Marathon Winters is a lot cheaper than a broken collarbone or lost time from work. The event that precipitated me getting studs was when I was riding down a long, gradual downhill in the bike lane - no more than 20 mph. It was about 20 degrees and bone dry, except that someone watered. I didn't notice the ice until I was getting passed in the nearest lane by a garbage truck. I didn't go down, but if I had, it would have been over.

You never know where patches of ice will creep up. Even plowed roads have ice patches.

Good studded tires will not wear down quickly, even if you run them on bare pavement 99% of the time.