I first heard of it over at Word of Shadow and soon after that I noticed it going on in some of the scenarios. The theory is you get a lot more renown if you make your own party for the scenario, and because you don't have to share any renown that 'you' earned you generally get a whole lot more then the rest of the peeps on your side. A lot of people in the game have said that they never heal those who make their own group to farm, and I know that if I was a healer neither would I. People may say that there is nothing wrong it or Mythic would have done something about it, but it seems to break a certain code in the game.
In my previous post I talked about the scenarios and how they differed from WoW's battlegrounds, how it was more important to get support your team and get the win then get the kills and damage, and I think this practice goes against that. Through the practise I've often seen these people at the top of the damage charts with a massive amount of renown, while the rest of their team had very little renown or experience having lost the match. Renown farming is selfish as the people care more about how they go individually in the scenario rather then how their team went (Whether they won or lost) as it doesn't effect them nearly as much. Then again, this entire post could be because as an Ironbreaker I'm useless at burst damage and can't farm renown myself...