These diff drop kits can be used to put your CV's back to normal angle or to allow a greater lift to be put in without maxing out the CV's
Normally the higher you lift an independent front vehicle the CV angle is increased. This increase in angle generates more heat and can lead to the CV prematurely wearing out which can be very costly.
A common application of this kit is with a 2" suspension lift coupled with an extra 20mm of lift from strut spacers to fix the typical "nose down" look the Hilux/Prado/FJ Cruiser have.