Other than it be annoying to see all the warnings at render time, it doesn't really matter... i was really more curious about the solution in the event i ever had mel I wanted executed at prerender time.
also... i never did a render speed test, but i have a scene with probably about 1000 warnings in it and I feel like it slows the render time down cuz its waiting for the prompt to write out all the warnings before moving to the next frame.