Plastic folders preorder bonus?

[CaptainCommando]

What exactly are these plastic folders I sometimes get when I preorder Japanese albums? I got one for preordering the Lament of Innocence and Curse of Darkness soundtracks together from CD Japan, and I recently got one for buying the new Studio Ghibli Songs album. These things are made out of durable plastic and have good-looking illustrations on them, but I honestly have no idea what they are used for.

[Crash]

Are they about the size of a piece of paper? I think those might be clear files, which are used to store papers, just like normal folders. When I'm working on projects, I like to separate different components in different clear files so it's easy to remember where to look. "Investment guarantees? OK, I need to check my Zwei!! clear file for that."