As the current extracted from Schottky diode is small enough to provide 0.3-0.4V voltage drop, PMOS's threshold voltage will decrease due to body effect. Thus, PMOS only requires small vgs to be turned on.
However, some people say this method is impractical or rare to see in low voltage IC design. I would like to know if there is any drawback when we use it in LDO. Thanks!