Much easier to overclock because of having an 'unlocked multiplier'.
So say a 940 BE has a multiplier of 15x and 3.0ghz speed, putting the multiplier to 18x would give a 3.6ghz speed (it goes up 100mhz for every 0.5 multiplier). You might also have to increase the voltages a little in order to keep things stable, but otherwise it's 'free' performance.
You can overclock non black edition cpu's too, it's just a bit more difficult.