Population numbers matter in many ways. Getting accurate projections of population counts for a city or a county can make or break a community financially and impact quality of life for a long time into the future.
Sure, no one has a crystal ball to foretell the future, but there are formulas and analytical models that can predict population numbers with great accuracy.
Accuracy matters, as underestimating population numbers can lead to inadequate roads and public utilities, and overestimating growth can mean paying for more infrastructure than needed.
Either way, a community suffers when population growth is not well-captured.