[pooriaazimi]

I'm no expert in this area, but maybe if you want to use mongo for logging? Or things like that.

I kinda like TCP vs. UDP analogy. Sometimes you care more about speed than precision. A few dropped items in a log. Not a big deal. I'd rather have that, than to be forced to use a more expensive machine for the job.

That said, I absolutely think the default should be the TCP way.