The balcony was defensible, he said, on the best grounds of architectural tradition. Scoffing at the idea that the balcony had been put on to provide an outdoor sitting area or, indeed, that he had time for rocking on a porch, he gave two reasons for adding it: first, to break what Truman considered the outlandish, disproportionate height of the portico columns, designed in Jefferson's day; and second to aid in shading the windows of the Blue Room. Dirt-collecting awnings could be done away with and neat wooden shades rolled up under the balcony, to let down when needed.

Reference:

The White House And Its Thirty-Four Families
by Amy La Follette Jensen
New York: McGraw-Hill Book Company
1965, p. 251