For example, user bough a template (capx or c3p file), or grab sub-system with some objects, events from old project, and try to paste them into another project.
Objects with "world" type like sprite could be copied and pasted very easy, but non-world object couldn't. Thus it is better to make all kinds of plugin with world type. Moreover, "world" type object could have behaviors to add more functions
Well, it is not a good suggestion I agree, but I have no idea how to support these features without changing current work-flow or IDE.