External References (xrefs) are an important part of working with AutoCAD and its vertical packages. I consider xrefs a critical and key feature of AutoCAD in the AEC industry and encourage you to look into them if you are not currently utilizing them on your projects. There are many aspects of good utilization of xrefs, but I thought I would list a few tips in this article.
Whether linking files in Autodesk Revit or xreferencing files in AutoCAD, choosing to Attach or Overlay is an important decision. As I perform software training at companies, I routinely encounter many users who do not understand the difference between using the Attachment or the Overlay options. There is not a global right or wrong answer to this decision, but understanding the difference helps you to determine which option to use to achieve the results that you require. When you link or xref a file into your current file, you are doing that to see information that is in another file. The Attachment/Overlay option determines how that file will be seen downstream in other files.
Autodesk has finally fixed a major wall cleanup issue between mirrored xreferenced drawings in AutoCAD Architecture!
Cleanup between overlapping walls in different xreferenced drawings was introduced several releases ago in AutoCAD Architecture (Architectural Desktop name at that time). As they continued to improve the feature, walls still had problems cleaning up properly when the xref was mirrored. If an existing xref was copied and mirrored, the mirrored version would have gaps in similar locations as the first instance of the xref. If an xref was brought in and mirrored (without being a copy of another xref), then the xref would not cleanup at all. Either way, walls in mirrored xrefs would not cleanup correctly with walls in other xrefs.