Now I remember why I added the option: doesn't the internal miner call CheckWork() if 16 bits are zeroes? ie. this message would be printed a lot for the internal miner, if added unconditionally, right?
That's what I meant when I asked "are there significant costs?"
If one of the mining pool folks think this would be useful in a production miner, then I see the value. If it is only really useful if you're trying to debug a remote miner that isn't working quite right...