That’s right, I called it “Junk”.
Recently we have been experiencing excessive bloating of files because somewhere in our project someone has either referenced in a drawing that was opened with Microstation or they have copied in something from a drawing that was used by Microstation.
When you start the PURGE command in AutoCAD 2015, you now have the option to purge “Orphaned data.” AutoCAD apparently handles Microstation linestyles and text styles differently so the info that defines these objects becomes “orphaned” and can bloat drawings severely.
Check the box as shown below
If you have any of this purge-able data, the progress of the purge will be shown in the lower right of the AutoCAD screen (shown below)
To purge the “Orphaned” DGN junk from your drawings using the command line version of PURGE command in a script or macro, use the O (letter O) after issuing -PURGE from the command line.
Note: after purging what could be a lot of data from a drawing, it is a good idea to AUDIT your drawing. In the command line, enter AUDIT [enter] Y [enter]
For more info about how to purge unused DGN info from your drawings, check out these links:
Autodesk’s hotfix for AutoCAD 2013 & 2014: http://knowledge.autodesk.com/support/autocad/downloads/caas/downloads/content/autocad-C2-AE-dgn-hotfix.html