One of the nice things about not having documentation is that only those that take the time to explore and learn can exploit the feature. On the contrary, when documentation exists, not reading it would put you at a disadvantage.
Why exactly is this "nice", but having features that can only be exploited by grinding XP and equipment drops is horrible?
I mean, yes, exploration is more enjoyable than grinding, but isn't that already its own reward?
Why does it make a game better to reward one kind of massive time investment, but not another?
In my opinion, putting options in a game for people who want to discover mechanics on their own and be rewarded for it is appealing. It goes along with the hacker mentality.
It's a subjective opinion...you don't have to agree with me.