My grandmother (she'd've been ~118, now) taught me to sew. There's specific techniques for turning down interior hems. That is, imagine a jacket: it has a shell, and a lining; I'm talking about a specific kind of hem for material between the shell and the lining. The finish work of that hem had no bearing on the quality of the item — it just demonstrated to the next tailor working on the jacket that you'd spent the time to finish the parts only they would see.

And, goddamn, it doubled the effort for finishing a jacket.