Why is the Hardy-Weinberg principle important, since genetic equilibrium seldom occurs in nature?

It is important for determining IF a population is in equilibrium or how fast (how much) change is taking place, since the equations can be used not only qualitatively, but also quantitatively and in relative terms. An even more important use shows the frequencies of dominant zygotes and heterozygotes in a population, which can be important in determining how prevalent a recessive allele is in a population.