Diff between "all papers" and "secondary" in google drive?

The majority of my saved papers (measured in bits) are in my “secondary” folder, but about 1/5 of my storage is in “all papers.” Difference is not immediately obvious (although it probably should be!) and I’m curious. Thanks.

re-upping this. the more you know!

Not sure exactly what the problem is. What is a “secondary” folder?