The WT uses "new light" to have it both ways.
On the one hand, it's used to posit that the organization leaders understand more now that anyone else did in the first 20 centuries C.E. -- the light has gotten brighter in the end times for those who are "in the truth."
On the other hand, it's used to excuse all its previous errors and to make the latest adjustments look like never-ending blessings and revelations from Jehovah to the faithful and discreet slave.
Thanks to this sleight of hand, the vast majority of JWs don't notice that until 2013 the faithful and discreet slave didn't know who the faithful and discreet slave was (Russell v. all the anointed as a group v. the GB) nor did they understand who the domestics were (the anointed as individuals v. the anointed plus all the other sheep) to whom they were supposed to be providing good spiritual food in due season.
Nor do they notice that it could all change tomorrow when the light gets brighter still and what used to be "the truth" turns into "old light" which needs to be dismissed and forgotten.