The scientific consensus on salt seems to be changing. I think that current thinking is that salt is unlikely to be a major influence on health, all other factors being equal.
There's a lot of evidence that ordinary healthy humans need a particular amount of salt each day (adjusted for activity, age, etc), with not much variation. There's some epidemiological studies that show that most humans do end up consuming that amount of salt - i.e. the physiological->psychological feedback loop that triggers the impulse to eat salty things is well-controlled.
Eating both too little and too much salt can lead to very major health problems.
Popular fads on salt in diet changes all the time though; luckily that can't stop our bodies (unlike problems with anorexics; junk food; sugars; etc)
Regardless of health effects, cooking with unsalted varieties (stock, butter, etc) allows you to control the amount of salt in your dish. You may end up with an over-salted meal if you use salted butter, etc.
