Concerns are useful when they're genuinely sharing functionality between classes I've found them genuinely useful for that - there is a lot of code for things

Concerns are useful when they're genuinely sharing functionality between classes I've found them genuinely useful for that - there is a lot of code for things like urls, publish status, ratings, roles, permissions etc that can be shared between models if they have similar functionality. They're just a recognition that composition via modules is often better than inheritance.