Waste of time? 99.9% of the time.
At the end of the day, Atheists cannot prove themselves right any more than they can prove their opposition wrong. So, what is left to be said? I think many of these discussion are just a desperate attempt to justify the atheist's position, so they can sleep at night. In a way, it comforts them.
Faith and belief are a personal matter, but why do the blind feel compelled to invite those who can see the truth to ignore their sense of vision and pretend that they haven't seen anything at all? Perhaps misery does love company.
Blaise Pascal's "Wager Argument" is correct:
If the atheist is right and God doesn't exist, then he gains nothing. But, if the atheist is wrong and God does exist, then he loses everthing, including his soul.
Conversely, if the Christian is wrong, and God doesn't exist, then he has lost nothing. But, if the Christian is right and God does indeed exist, then he has gained everything including eternal life.
Pascal then summed it up by stating that the prudent man will choose to believe in God's existence, if for no other reason than he has nothing to lose and everything to gain.