It's one of those "obscure", old-timey things ... there is a learning curve and it is a little "futzy" ... BUT ... the results can be well worth it.
One of my Martini Henry .577-450s, a Mk-III with a .465" grease-groove bullet, shot poorly (leading after about the 5th shot). I resized some bullets to .451" and paper patched them and HOLY COW!!!
I had 10 rounds loaded, the first 3 or 4 were so-so accuracy, not exactly where I was aiming ... but all were "round holes. Then ... something began to happen ... a hit, low, but centered. Then for the remaining rounds, using "Kentucky Elevation", I walked them right up into the target!
That sold me on the value of paper patching. I now look forward to Winter when I've found the humidity level to be just perfect. I do my patching on a glass-topped desk which is simply ideal for rolling and finishing up the base.
A good read about the mystique of it all is Paul A. Matthews' "THE PAPER JACKET".