>> ...by halving the ISO of a film, the negatives would be more accurately exposed.(posted 9033 days ago)Rubbish. It is important to find your own EI, and this might happen to be one stop slower than the ISO speed, or one-third or a stop, or even perhaps faster. Once you have found the correct EI, you should stick with it.
The only merit in always using half this EI is that you will then err on the side of overexposure. This is better than underexposing, but it is even better to get the correct exposure.