A lot of articles say once the cam and lifters are successfully broken in, the ZDDP is not critical. I disagree, because most of the time anyone concerned with such, has a better than stock cam with higher spring pressures. I think in those instances, it is certainly beneficial to continue the use of ZDDP. I know I have and I will continue to do so, regardless of anyone else's opinion.
Those articles about flat tappet cams are written by kids right out of college. Probably never new what a real hot rod is!! Especially one with a hydraulic or solid tappet cam. Their info is useless.