https://www.youtube.com/watch?v=XRuKKchj7sk
Properly set up, it might eliminate the need to turn off the swaged donut around the base when doing "extreme" case forming. That extra material could be nibbed to lengthen the case; say, if one wanted to make .22-15-60 or .25-25 cases out of something more readily available. The web around the primer pocket would be soft, for sure, but might not swell too badly at blackpowder pressures.