Why is the Hardy-Weinberg principle useful in spite of the fact that its conditions are never met in natural populations?

The Hardy-Weinberg principle is useful because it provides a baseline value for genetic equilibrium. When researchers are examining the frequency of alleles for a particular gene in a population, they can use the genetic equilibrium value as a benchmark to see how different the frequency is in a natural population. The skewed allele frequency can provide evidence of selection and evolution.