How is the DNA molecule model useful to scientists

how is models of the double helix DNA molecule structure useful to scientists?

its the genetic blueprint of all living organisms on earth
its the code or information for every part of the living thing
for example your DNA would contain what color eyes you have, how many fingers you have, etc

It can be useful in genetic engineering/genetic modifications. Examples:
-getting cold resistant cells from an alaskan salmon and putting it in corn/potatoes so they grow better in the cold
-mixing a grape with an apple
-making corn sweeter or grow bigger
-cloning people/animals
-curing diseases in people
see "spidergoat"