Each position on the long molecule can store twice as much data as one bite of computer code, and that only improves once you consider multiple locations. Three is a magic number, since three adjacent bases specify one amino acid, the building block of proteins. This poorly understood junk is generally considered a heckuva lot less interesting than the DNA that codes for proteins. We like to compare nonsense DNA to the ads that foul up sitcoms, say, or cop shows. But DNA fingerprinters are obsessed with junk .
Genes make proteins, but proteins work only when patterned on a good DNA template.
So the DNA in genes must stay essentially the same generation after generation. Changes are called mutations, and most mutations are harmful. Fortunately, junk DNA is exempt from the need to remain identical. Like an ad on Ally McBeal, it can change, and nobody will notice much. In repeats, short sections are duplicated.