HWE is used with COIDS and non CODIS eligible DNA profiles to provide statistical caluclations for the rarity or uniqueness of profiles. Each STR kit test for a certian number of loci. Each lous has a set ladder of observed alleles. Each of these alleles has value for its observed frequency in a population. It is the rarity of each allele at each location that will give you the value for rarity of the profile as a whole. This rarity fo the profile is calucalted in CODIS under certian circumstances using to determine the eligibilty of a partial profile or a forensic mixture to determine its eligiblity for the different leves of the database.