Here are some answers:
Potential Issus with Importing/Linking dwg (CAD) files into Revit
- Corrupt dwg
- Large file size and extraneous information
- Linked CAD can become unlinked but will still display. This can cause confusion as to what the latest file is.
- Possibility of someone exploding, causing up to 10,000 extra elements.
- Many AutoCAD layers and linetypes are brought in after an explode
- Size of CAD needs to be under 20miles in diameter. There can be items which are not part of the primary drawing that are very far away from 0.
- Visual clutter
- dwg files from programs like AutoCAD Architecture and Civil 3D may need special plugins to see all of the data.
More Issues...
What Can be Done
In AutoCAD:
Wblock only necessary information
Purge
Audit
In Revit:
Always link, don't import
Current View Only (for 2D dwgs)
Detailed explanation here for Survey drawings
Importing and Linking CAD Best Practices part 1
Importing and Linking CAD Best Practices part 2
Imported 3D AutoCAD not Sectioning