I personally use sarcasm far, far too often. And when I sit back and reflect on those times, I am completely certain that it never advances my point farther (vs. the same point made without sarcasm), never makes my point seem more clever, and never makes my point seem more funny.

So why do I continue to do it? Honestly, I don't know. It is a completely valueless communication strategy, and I continue to use it. The best answer I have is that it's a self-protection mechanism, which seems better-armored against a hostile audience than if I made my point with sincerity. So I, personally, will try to do better. But I would also caution anyone with less entrenched habits to consider carefully whether sarcasm is a useful rhetorical tool.