1) It encourages everyone to run everything on elite as this maximizes XP as it relates to a bravery bonus.
2) It prevents newer players who are skittish about running elite content – because now elite is the most popular level to run things on - from joining groups.
3) It discourages grouping because if someone wants to create a group to run hard or even normal content, people will not join because doing so will break their streak.
4) It disrupts groups that have already formed when they make changes to the level of content they are running before they go in.
Item #4 is the most obscure, but I can’t tell you how many times I’ve seen groups go bad due to BB. A group forms, and they advertise hard or elite. They get maybe 4 players to join overall. Not having a full party, the majority decides to run it on hard. One or two people get upset that this will break their elite streak. An argument ensues, two people drop group because they are not doing the run on elite, and the group dissolves.
Everybody – and I do mean nearly everybody – is running stuff on elite, unless they are doing a favor run. The days of just plain flagging are all but gone. I don’t see a whole lot of loot runs advertised any more (over level, but running for loot and for fun).
Now, I do see a lot more faming runs these days. Lots of stuff advertised as “h/h/h/h/h/n”, but that’s because they’ve already tapped out elite on their streak. So, you can maybe join a farming run, and run the risk of causing a big dust-up over a 10% penalty because you died accidentally in a zerg run and the farmer is all bent out of shape over it…or…you can solo.
Honestly, I’m not the XP farming type, and really have no love for zerging quests. And I’ve had enough of those to basically discourage me from joining them except on rare occasion. You get some farmers who aren’t concerned about deaths, and you get more than a few who blow an O-ring over someone dying, and start harassing them.
With a BB, there is far more of an incentive to farm XP and level fast. If you create that incentive, people are going to exploit it to their own ends, and not in the way that some intend it to be used. Hence the plethora of farming runs, elite runs, and so on.