It dictates which makes more sense for me. As I'm on a very restricted budget I can either buy a .32 cal Traditions rifle, or I can buy a barrel for my Lyman's.
A .40 cal 15/16" barrel that's say 20" long might not be too heavy to be concerned about. And since I am fond of a .36 cal '62 Colt that avenue may be worthwhile.
I've often read of the complaints of the small calibers being harder to find an accurate load, as well as needing swabbed much more often. Though I've also seen contradicting claims, and therefore I'm not sold that it is just harder to work with, I do still like the idea of needing to buy one less mold, and to stock up on cast RB's for another caliber.
I like simple and multipurpose. But if a .380" RB isn't likely to work well in a .40 cal than it's not worth considering, and puts me back at a Traditions rifle and needing 2 molds.
And I'm not even at the point of making this jump, but I do like considering my options and whatnot. And I had initially looked at finding someone capable of a custom barrel made to shoot either a .380" RB or .320" RB as I was also eyeing a '63 Remington.