Oh man, I am not sure that information will be a help or hindrance to those not already familiar with sprintf and the murky consequences of buffer overflow.
It's worth re-emphasizing that its really easy to overflow the buffer, the compiler gives absolutely no warning of this and the runtime consequences are difficult to predict. Its about the worst thing that can happen if you are trying to debug code that isn't working.
Unless one enjoys living dangeriously, or is in full command of how the sprintf arguments will be expanded, my advice is to spend a few extra seconds typing those compound Serial.print statements 