Matt Murphy showed this tip in a class at Autodesk University. He explained that AutoCAD attaches XData to objects in drawings and this data allows information to be associated with specific objects. The problem is that when objects that contained XData are deleted from the drawing, the registered application becomes unreferenced. If you get a large amount of unreferenced registered applications in a file, it can increase the file size and cause sluggish performance.
The only way to purge these unreferenced registered applications is to access the Purge tool from the command line. Type -PURGE on the command line and you will see this:
Enter type of unused objects to purge [Blocks/Dimstyles/LAyers/LTypes/MAterials/Plotstyles/SHapes/textSTyles/Mlinestyl es/Tablestyles/Visualstyles/Regapps/All]:
Then type R (for “Regapps”) and it will prompt you with this:
Enter name(s) to purge <*>:
Type an asterisk (*) to purge them all. It will then ask you if you want to verify each registered application name to be purged. I recommend typing N to speed up the process.