When refactoring a schema, a change may have knock on effects in other parts of the schema, this dialog shows these changes.
Examples
If the name of a global type (i.e. a complex type) is changed, then the change is also made in all the places it is referenced, in order to maintain the integrity of the schema.
If the a global type (i.e. a complex type) is deleted, then all references to it are also deleted.