A natural key serves two complementary purposes: The uniqueness constraint assures uniqueness of data within a certain technical context (e.g. a set of values in a table, file or relation variable) by rejecting input of any data that would otherwise violate the constraint.
This means that the user can rely on a guaranteed correspondence between facts identified by key values recorded in a system and the external domain of discourse (a single version of the truth according to Kimball).
The advantages of using a natural key to uniquely identify records in a relation include less disk space usage, the natural key is an attribute that is related to the business or the real world so in most cases, it is already being stored in the relation which saves disk space as compared to creating a new column for storing the surrogate key.
Another advantage of using natural keys is that it simplifies enforcement of data quality, and they are easier to relate to real life while designing the database system.
In other cases, this can prevent improvements of the system altogether due to too extensive effort required for the change, e.g., the inability of the knowledge management software Confluence, to represent multiple pages with the same title.