It can be, if your water doesn't get much dilution. If you are using bleach or chlorinating liquid as your primary source of chlorine, then for every 10 ppm Free Chlorine (FC) that you add, you also increase salt by 16 ppm (8 ppm upon initial addition and then another 8 ppm when the chlorine gets used up).

So if you are adding around 2 ppm FC per day, then that's an increase of almost 100 ppm salt per month. If you have a larger cartridge filter, so no backwashing and minimal cleaning, don't have much splash-out, and don't have rains that overflow the pool, then the salt can build up over the years.

You can dilute it by partial drain/refill.

Richard