Probably good stuff as my wife swears by it... Maybe not so much engine related, but it keeps the colds away and/or shortens them she says. Also it creates a bond in the engines to help the oil stick to important parts within.
Good for engines with flat tappet cams but not much else. Some argue that it is not needed at all, but it's cheap insurance. The EPA has stripped ZDDP from pretty much all non-racing oils.