Originally Posted by
sinc
It's designed to deal with the problem created when new linework is added to an XREF. For example, you create a plan set that XREFs in a base file. The plan set is finished, but the project is not finished. So you continue working, and add more stuff to your base file. Now you need to print out that early plan set again. If you simply print it, it will contain all the new linework you added to the base file. This might cause problems, such as text overtyping, and it might be data that is not supposed to be in the early plan set. This feature is designed to warn you of that.