Almost every feature is a good thing. But the total quantity can become a bad thing, because the interactions between the features become more and more complicated. It's almost like features have values proportional to the number of features, but they have costs proportional to the square of the number of features. You eventually reach the point where new features add more cost than they add value.

But it's not that simple, because each new feature adds value to a subset, but adds costs to everyone. If the subset is vocal, they often get what they want, even if it's a net loss for all users taken as a whole.

So the trick is, first, to stop adding features once the costs outweigh the benefits, and second, given that you have only a finite number of features that you can add before you reach that point, to add the total set of features that are going to make the most valuable language.