Comment by kqr

Just last week I was hanging photos with my wife in our home and after she had proposed a placement I told her "I don't like the balance of the negative space there". I could have said "I don't feel like the parts of the wall not taken up by photos are balanced there" but "negative space" is a convenient abstraction. (Note that this is different from the photos themselves being unbalanced, which is also a concern but was not a problem then.)

Think of it like a foreach loop. Sure, it's equivalent to the corresponding for(;;)-style loop but it's also a convenient mental shortcut.