I normally don't add much salt to my cooking, but during the summer when I tend to sweat a lot, I've started adding a little to my cooking.

Sodium Chloride tends to be extracellular, and thus would show up in blood chemistry.
Potassium Chloride tends to be intracellular, and thus more difficult to estimate.

I'm not sure if it makes much difference, but I've started adding a little Potassium salt when I use regular salt. (No Salt).

As mentioned, your kidneys are very good at regulating body salt. So, strict salt regulation is probably only important in a few people in which the kidneys aren't effectively regulating the blood levels.

I'm not sure why urine salt tests aren't performed more frequently. I suppose due to the high variability in the levels. But, that would be one of the tests for hyponatremia.