If you work with e.g. Inventor and Windhill there will be problem if any of the dependent models for an assembly is removed (or missing) from workspace. The model will fail and the user must search the missing models in common space and manually add them to the workspace.
A similar problem appears when you want to replace a component in Inventer becouse you can't browse into common space right the way. You can only look in the workspace or at your local disk.