Thanks. Those are both helpful.
I noticed that if you save a project with a sandbox (and have operations in that sandbox) it will cause a run error (because there is no data in the sandbox once you close the project).
Just wondering why EM is programmed in that way - surely a sandbox should be treated as a table that does not run if there is no data in it? This is especially relevant as we using it to avoid saving false filters - its still a preferable approach of course, but just wondering as to why sandboxes can cause projects to fail - should they?