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.
What Can be Done
Wblock only necessary information
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