I guess I've been the lucky sort here. I've had a couple balls/bullets in my sidelocks that were either dry balled or either the powder got wet or contaminated for whatever reason. So far I've never had to use this method and was almost always able to get them out with just a ball puller (screw) on the end of my ramrod. I wouldn't be able to do that with a poly tipped bullet and will remember this for future reference.
I did have an instance where the bullet puller wouldn't work and I got it out by removing the nipple and adding about 20 gr of FFFFg into the snail, replacing the nipple and shooting it out into a dirt bank. That was my only option as I was up my cabin in the middle of nowhere and only had the one rifle.