The sale of war bonds "sterilized" the otherwise humongous U.S. debt. That is, while debt was historically large (by any standards except today's), we "owed it to ourselves" and not to foreigners. Which is to say that the money was available to be "recycled" into the U.S. economy after the war.
But the main benefit was AFTER the war. The country saved something like 25% of its GDP annually during almost four years of war. When it ended, the average American family had almost one year's wages in savings, most of it in war bonds.
That financed the greatest peacetime economic boom in American history, and allowed for returning soldiers to be employed in civilian pursuits, at higher productivity rates than they enjoyed before the war.