Not exactly sure when DC stopped installing the CAD or why. Some owners like it, some are glad they don't have it. The arguments vary but there is no specific reason to get rid of it, nor to wish you had it. Here are some pro's and con's of the CAD:
With CAD:
-You can install a '2 wheel-low range' kit, which allows you to shift into 4x4 LOW range to take advantage of the gear reduction of the transfer case for maneuvering heavy trailers into tight spots in reverse gear, without slipping the clutch so much. (manipulates the valving in the vaccuum lines going to the CAD so it doesn't lock the front axle in 4x4) Cool mod.
-you cannot install a locking or limited slip diff in front axle (DANA 60) unless it's the ARB Air Locker
-CAD considered by some to be a 'weak link' and prone to fail or not operate when needed (due to the added hardware, and vaccuum lines that can be damaged when off-roading)
No CAD
-Your entire front rotating assembly, ie, gears, axles, ring and pinion, driveshaft, transfer case internals, are spinning even when you're in 2WD. Not much of a 'wear and tear' issue, but there is a bit more drag. Probably not much to worry about. Slight MPG penalty probably.
-Cannot install a 2WD LOW kit
Read this duscussion for more arguments for and against CAD.
https://www.turbodieselregister.com/forums/showthread.php?t=40881&highlight=CAD