I understand that to be a general recommendation, but I disagree with it from research and personal experience.
Some lift kit manufacturers have stated that the CV angles are not severe with the added 2-3 inches of front lift and that the front diff drop is really not necesssary and no longer recommended. I happen to agree with those statements.
I've installed the front diff drop multiple times, and compared CV angles. Even though they are 1 inch drop spacers, they don't lower the front diff by 1 inch, instead they rotate the front pinion angle a few more degrees upward (unnecessary) and add only a slight amount of overall lowering, perhaps 3/8 of an inch, which has very little effect on sparing the CV angles from significant wear and tear. Vibration and droning complaints are fairly common with the front diff drop which is why I checked to see if he had driven it without it. FWIW, I had almost 90,000 miles on my old lifted 05, with no diff drop and no CV issues, and 35,000 on my lifted 07 with no diff drop (that's a whole other story) and no issues. I also have a 1-piece from Tom, great investment.
I would make correcting the rear driveline angles top priority. It usually results in reduced or at least more acceptable levels of vibrations, without the front diff drop. Just my 2 cents.