Whenever you try to copy an event sheet from one project to another, you'll get an error dialog if you're missing an object in the new project.
The only problem is that it'll show you only one object at a time. If you're copying an event sheet from a relatively complex project it becomes a bit of a pain to copy it to a new project because you'll be figuring out the objects you need to copy over one by one. It'd be much easier if you could get a full list of the missing objects when the copying fails.
Of course, you could just copy all the objects from the origin project into the new project, but it'd be ideal to not have to pollute the new project like that.
I've mostly ran into this problem when integrating templates (i.e. a dialogue system template) into my main project, where usually the template project has a lot of object that only serve for an example layout which I rather not add to my main project.