I don't get how this is even a question, leakers and leaks have never been thought of particularly fondly, at best they lead to no negative effects on games, gamers, and game developers, and at worse can have a neutralizing effect on the sales and hype of a game reducing the likelihood of another coming and reducing the chance of a pay raise for PR people and possible the happiness that devs could get from seeing people raw reactions to their creation and puts a damper on the efforts of near a hundred people and could lead to layoffs.
I could go on and on about potential effects that leaking can cause, however I think most of us already know all this, though even ignoring these perspectives don't you think that the reaction to Mario and Rabbids would have been far more interesting if it hadn't leaked, like I could see it even becoming the highlight of this years E3.