Playing Black and White will help you understand what is going on in Black and White 2, since their stories are connected, and beating the game will let you sync your save file with BW2 to unlock memory links, which are pretty much in-game cutscenes that reveal more about the story.

But unless youre a huge pokemon fan that has no problem playing both games back to back, it probably isn't worth it to play them both. If you don't care about trading your old pokemon to the new game, or using memory links, or even about the story, then it's probably not worth it to play BW.