Negative space is the space in a design that’s not filled up with stuff. It is also referred to as white space, whether it is white or not. The shape of your negative space should be as visually pleasing as your positive space. Space also communicates relationships between page elements. A little bit of space between things means they are related, and a lot of space means they are not. (See also Group Similar Content Together.)
Proper spacing is vital to readability and content prioritization. Plus white space is simply restful to the eye.
Why Negative Is Positive in Web Design by Rob Bowen