As long as we're talking safety. The only major accident we've had in my time in the shop happened on the rare time when I took a day off so I only got second hand accounts. A student was polishing a bbl blank in the lathe with a three jaw chuck on the breech end and a live center on the muzzle end (4 or 5 contour centerfire cro-mo blank) He mistakingly set the lathe to 2000rpm(his claim) and forgot to lock the quill of his tailstock. When he started the lathe the live center backed out and the force of the bbl spinning threw it off center smacking it off of the ways and hit him in the arm 4 times before he could get away from it. It broke his arm and his hand and took some really big gouges of flesh out. He got got about 4 steps away from the lathe before he collapsed on the concrete floor. As a consequence, if someone wants to turn something like that between centers, they have to limit their rpm and use a faceplate and a dog so if the center in the tailstock does come loose it will just drop out.