Some individuals tend to be more salt sensitive

Considerations for Specific Population Groups

Individuals With Hypertension, Blacks, and Middle-Aged and Older Adults.  Some individuals tend to be more salt sensitive than others, including people with hypertension, blacks, and middle-aged and older adults. Because blacks commonly have a relatively low intake of potassium and a high prevalence of elevated blood pressure and salt sensitivity, this population subgroup may especially benefit from an increased dietary intake of potassium. Dietary potassium can lower blood pressure and blunt the effects of salt on blood pressure in some individuals. While salt substitutes containing potassium chloride may be useful for some individuals, they can be harmful to people with certain medical conditions. These individuals should consult a healthcare provider before using salt substitutes.
http://www.health.gov/dietaryguidelines/dga2005/document/html/chapter8.htm

*Salt related health problems:
http://www.saltmatters.org/site/index.php?page=salt-related-health-problems
http://www.saltmatters.org/site/uploads/PDFs/SRHP%2025+table.pdf
http://news.bbc.co.uk/2/hi/health/3312667.stm
http://news.bbc.co.uk/2/hi/health/6680185.stm
http://whyfiles.org/111salt/