That bearing on a stick you used to true the face was shown to me many years ago, and I have saved a lot of setup time with it.
But there is another application I have used it for:
Chuck your shaft... end chuck... get the shaft turning and crash into it with trusty bearing in a stick.
Trues stock for subsequent center drill.
Start with moderate chuck pressure, when she is running true, tighten down.
If you accidentally cut a sloppy screw thread, put this in the tool post and actually roll down the major diameter of the screw threads... swageing them as you go. It might take you from a 70% to a 60% but sometimes that isn't too important.
Just beat down the top of the thread form....
And another, in straightening bent shafting...sometimes heat is used, buy push the bearing against the shaft between centers, and throw it in feed.
Keep your hands on the cross-feed and keep consistent but not excessive pressure against the shaft.. you could hurt your lathe.
But it works that shaft back to straight.
