White space isn't simply the space left over from black type. It isn't, or shouldn't be, an inert background. There is a lot of power and potential to be exploited there.
Sometimes we use it as another form of punctuation. Allowing the reader to more easily discover the breathing pattern of the poem. Traditionally this exploitation of white space was used mainly in stanza breaks. But poets have found a multitude of uses for it.
One reason for exploiting the white spaces is that it can bring the whole page alive, carry hidden meanings and stretch the imagination of the reader. Used well it enriches the reading experience and helps the reader better understand the message the poet wants to convey.
Read some of the work of ee cummings and you quickly see the multitude of poetic devices he used.
The most familiar (for cummings) is a dislike for using upper case letters. However enjambment and caesura, as well as the clever use of white space, are also tools used by cummings to great effect.
So the next time you look at a blank page and prepare to write remember that part of your poem has already been composed! You merely need to place your words in the right pattern to allow the white spaces to live and breathe.
Author of Dry Bones http://amzn.com/B00AAX3N7E
& Under The Dog Star http://amzn.com/B00E64XY2M