I use OmniFocus for home and work, and use the focus feature to keep my projects separate. Every now and then when I unfocus for some reason, I’ll find a few projects that have gone missing because I had taking a task and used “Convert to Project” and it was placed at the root level outside both my home and work folders.
I realize that the focus might currently be all the way down to the project level where it doesn’t make sense to add a new project, but at the folder level it would be very useful to keep projects from getting “lost”.
Consider adding a repeating action that prompts you to check for any root-level projects. I group these sort of maintenance actions in a System Maintenance folder that’s separate from work, personal, etc.
To make this more convenient, you could create a “Projects - Unfiled” perspective. This is one of the perspectives that I included in the Custom Perspectives Directory of my Learn OmniFocus website: