Actually, you can lower a 4WD if done correctly. Rear axle is exact same lowering with flip kits/blocks as a 2WD. You may have to shorten the drive shaft.
The front is the most difficult. You will need new drop spindles, and if torsion suspension (GM), you will need new torsion keys, and a professional to re-align your front transfer case, and possibly shorten your front drive shaft from the transfer case.
Why would you do it? Well if you want the additional capability of handling snow driving and/or slippery ramps, but still want a slammed ride, yes, it is feasable. Look at all the lifted trucks in shows now. Probably 1/3 of them are 2WD 'desert runners' just built for show, no go.