When a DWG reference (xref) is unloaded from the current drawing, the drawing opens much faster and uses less memory.
When an xref is unloaded from the current drawing, the drawing opens much faster and uses less memory. The xref definition is unloaded from the drawing file, but the pointer to the reference drawing remains. The xref is not displayed, and nongraphical object information does not appear in the drawing. However, you can restore all the information by reloading the xref. If XLOADCTL (demand loading) is set to 1, unloading the drawing unlocks the original file.
You should unload a reference file if it is not needed in the current drawing session but may be used later for plotting. You can maintain a working list of unloaded xrefs in the drawing file that you can load as needed.