I had never heard of them either until I read a piece by Chuck Hawks (I think!) He explained that they help equalize pressure giving you more consistent velocities and therefore more accuracy. He went on to say that the old timers would use bits of tobacco, grass or wasp nests as a wad. All I know is it improved my groups.
I shot a Traditions Deerhunter.50 cal. with a patched roundball since the 80's (1:66 twist). Took Deer with the gun... missed or misfired on multiple times what I took of course.
Fast forward to last week. I bought a Deerstalker from a member last Thurs (Retiredusne8). Took it to the range Saturday. Being comfy with Patched balls, and having a gaggle of lead, that's what I used. Book said 90 grains FF with a .50 PRB so that''s what I used. Took 5 shots off a bench at 50 yds. 1st was 8" high, 3" left, and the next 4 shots I tweaked a bit on the rear sights (windage/elev. to where the last shot was zeroed in 1/2" high and centered.
Most impressive however, was the ignition on this sucker. My Traditions I could never find a good ignition combo. Retusne8 hadan Black English Flint in it, and that's what I used. Honestly, there was no noticeable delay on ANY of the 5 shots once the flint hit frizzen. I was IMPRESSED. primed with FFFF. I also picked and cleaned pan between shots.