I've heard that a lot of the scrap collected during WWII wasn't used for anything as it was just that... Scrap. Only the copper, newspaper and rubber was of any real use, while aluminum proved almost useless.
While it had only limited affect on the war effort, it was certainly a morale boost for the citizens of the U.S. whom thought they were providing value service to their nation. The only tragedy was the number of historical items, such as antique gates, old bells, and Civil War canon, that were uselessly sacrificed for the war.