The Rule of Space
The rule of space is applied to visual arts like photography, graphic design and illustration to provide a room for visually moving objects or simply to let the eyes of the viewers rest.
This can be achieved by leaving empty space around your subject or in your artwork.
The empty space is commonly known as lead room or white space depending on what field it is used.
Lead Room and White Space
In photography, videography and other forms of visual arts like sculpting and painting, the space in front of a stationery subject or in the direction of a moving subject is called lead room (sometimes nose room or active space).
In graphic design, illustration, desktop publishing and other similar fields, the portion of page that is left unmarked like margin, gutter, space between columns and other parts which are visually empty is called white space.
Take note that white space is not necessary to be white. The term came from printing process where white paper is generally used.
Positive and Negative Space
However, in more specific classification, white space (literally white) is referred as negative space and colored space is referred as positive space.
In photography and other similar field on the other hand, the space in front and in direction of the subject is called positive space, and space at the back and the opposite direction is called negative space.
The Significance of the Rule
In general, your composition is more pleasing and effective of the rule of space is being used.
As mentioned above, it also provide benefits for the viewers especially in the field of graphic design where a message should be accurately understood the audience.