Just to be clear, I never suggested that formula as a way of estimating a current cloud-base. Obviously METARS or some instrument would be better.
However, unless you live next to your aeroplane and can fly at the drop of a hat, it can improve the odds of actually flying by helping to choose days to free up for a flight. Fronts and isobars on forecast MSL Pressure charts are useful too.
Of course the TAFs on the day will be different, that's why we look at the TAFs before we fly.
