I'm sure this will help to answer your question. I had an advertisement for an exhibit about the Bable placed inside of my library book by the county library. All the books in the ordered book section had this ad. See ExplorePassages.com for details if you are interested but be prepared to get nauseous.
I think this quote from Sun Tzu's "The Art of War" sums things up perfectly for me:
"So it is said that if you know your enemies and know yourself, you can win a hundred battles without a single loss.
If you only know yourself, but not your opponent, you may win or may lose.
If you know neither yourself nor your enemy, you will always endanger yourself."
I feel reading the Bible gives you a fully understanding of just who/what your enemy is and makes you more prepared when having a discussion with a X-tian.
Christianity is not the 'enemy' always and/or everywhere, yet it is good to know it's literature to be able to understand the effects that Christian thought has on current politics. Depending on where you live it might even be considered vital to know the Bible to understand the politics and people of your own country. Even though Christians themselves have not always read the Bible and are often the first to tell you that they do not understand (all of) the Bible, the Bible does influence many a religious organization and person in power.
As a non-native English speaker I can also recommend people that do not speak English as a first language to read the Bible, specifically the King James Version, as it will allow you to better understand the English language. I think that it's one of the most influential books in history in regards to literature and even today we still use many a proverb from the (KJV) Bible.
Knowledge of the Bible is indeed one of, if not the, best 'weapon' an atheist has when debating/discussing with a Christian. A theist worst enemy in any discussion is an atheist that knows the literature and/or dogma of the theist's religion. Theists cherry pick from their religion and when confronted with the less then appealing parts of their supposed holy dogma or the inconsistencies in it, will often either actively or passive concede the discussion.