After some types of foot or ankle surgery there will be hardware used such as screws or plates. When removing the screws it can be helpful to plan out the exact location of the head of the screw so that the skin incision can be smaller and more precisely located. Therefore there often is faster healing with a smaller wound (and scar) and less postoperative symptoms or pain.
So I often use ultrasound imaging prior to the surgery and map out the location of the screw head. I also sometimes will use fluoroscopy and place a metallic reference-object over the skin when I do the floroscopic image. Again with either one I can plan ahead prior to surgery for shorter surgical time itself and a less involved procedure.