Of course, this is simple logic =)

This is the base of the Lean Manufacturing theory as per Toyota. 

Backlogs are also “stocks” (of stories).

The thing is, somebody needs to write those stories. Sometimes, they badly come with details (someone thought of!). Then, if you’re into scrum, bang, someone needs to evaluate it.

Then they’re here, hanging on the wall, waiting for someone to pick them up. But done stories change the whole story, like, let’s say, always. And then you need to change those stories. Sometime to remove those stories.

This is simple logic. Big backlogs, big waste.