Why is salt bad for you?

Not necessarily: Your body is bathed internally in a salt solution so you need some salt ingestion all the time. Data suggests that too much salt can lead to hypertension which has unfavorable effects on the heart and vessels. So in these cases a low salt diet may be recommended.

Fluid retention.: Salt can raise the blood pressure, so would be particularly bad for people with high BP. It also causes water retention, so could be bad for people with CHF or kidney issues.