I've got two stories from several years back, actually both came in the same year.
Arkansas Youth hunt: Very cold morning, temps not much above 40 with a pretty stiff wind. We drew a hunt in Holla Bend. A turkey gobbled from the roost pretty early, so we were able to get setup quick. He flew down and ran into our setup stopping 20 steps away, but James couldn't see him due to a bush. The gobbler, plus a hen and jake, stayed within 100 yards of us all morning. My brother, who was taping the hunt had to leave, so he snuck out. After about 30 more minutes of freezing, I asked James if he was cold and of course he was about frozen. I decided to do the fighting purrs to see if that would get things going. Using a mouth call and a Primos crystal, I gave it the best I could. All 3 turkeys came running into our setup again, with the gobbler not giving him a clear shot, so he killed the jake. It definetly worked this time.
Missouri hunt later that same year: We were on several turkeys who had given us the slip the last few days. They would gobble from the ridgetops, only to fly down and head toward the hollers, shutting up. We made several circles without striking a gobble, so we decided to put on a mock fight. With mouth calls and friction calls we put on a wild sounding schoolyard brawl and had two gobblers fire back. One turkey gobbled about 3-4 times, while another got fired up. We crossed a steep holler and got setup just in time to hear him gobble at less than 40 yards. He came in and gave Brad a perfect shot. Without the fighting purrs, we probably wouldn't have gotten him.
Several other times I've used it to get turkeys to gobble, but have not had the same luck getting them in as the two stories above.