This equation computes the hyperfocal distance1, the nearest focus distance at which the depth of field extends to infinity. If you focus a camera at the hyperfocal distance, the resulting image has the largest possible depth of field for a given f-number.
If you focus beyond the hyperfocal distance, the far depth of field does not increase because it already already extends to infinity. if you focus beyond the hyperfocal distance it does decrease the depth of field in front of the subject, which decreases the total depth of field.