I think most people buy the .45-410 barrels to use only in the scattergun mode. That is, after all, what it truly has to offer. If you feel the need to justify it, this barrel set-up does have some applications for small game and "close quarters varminting" for lack of a better term. Some guys (not me) have become fairly proficient busting clays with them. I've seen a guy shoot a quail with one, but it was a once-flushed preserve bird and wasn't flying all that great. The guy IS an exceptional shot, though. I also know a man who claims to have killed a turkey with one, although I didn't witness this feat.
The main thing is that they are just plain fun to shoot. I think shooting pattern boards with a shotgun is kind of a drag. Shooting patterns with a Contender or Encore with a .45-410 barrel is almost a guilty pleasure. Everyone I have ever allowed to shoot mine agrees that it is a hoot.