Lucylee, you're right, the papers would slide out if one wasn't careful. I only carry it back one hallway to the file cabinet back here. And I don't leave it out either. I have a shelf ankle-high under my desk and it rests there until I need it, then I empty the letter tray I use for keepable filings and sort and load into files and then put it away until next time.
They have 9x12 ones that are more binder type instead of a long narrow strip like I have. I think the papers would stay put better in that one.
I use an a-z expandable folder (the old red-rope type) to use for subcontractor insurance certificates. That works well, except it was feeling a bit flimsy to keep getting out of closet all the time so I put it into a plastic "milk crate" type container where it just fit exactly.
I guess the most important is to have a space to set up where you'll work and keep things. I'd get rid of couches and chairs before I'd get rid of my desk!