It gives a little more flexibility. its a good option to have . if I'm not mistaken if your talking strictly phenom's II and not Athlons the current line up is priced so a BE Phenom is the obvious choice. With Athlon's II you lose the cache and BE (unlocked muti's) but people have almost the same success with those.
1- BE: Black Edition, means, unlock multiplier. This processors are specially for Overclokers. Easy overclock, like my 955 BE, just with rise the multiplier can get the 3.6GHz.
2- Not BE: Lock multiplier, more dificult rise the frecuency. For people that use her PC at stock frecuency and never think in OC.
Now, the question is. Are you in the firts group? or the second group. If you want learn how OC your PC an CPU, buy the BE edition, but if you think all the games at stock speed don't buy the BE.
What? I'm pretty sure most people who don't have BE's but still want to OC can do it. BE's are just for convenience's sake or for easy OCing. Look at all the people with i7 920s, they don't have the extreme edition, but they can still OC the crap out of their CPUs.