What is black salt commonly used for?

They are used in salads and dishes. They have good antioxidant properties as well.

I know that it is used in making paani (for panipuri/golgappa)…

Sendha Namak and Black Namak where extensively used in indian kitchen till sea salt was imposed on us .
Both the salts were and are still used by some in cooking, salads, fruits . home remedy as it has medicinal value also.
Eating sea salt is slow poison whereas the above 2 salts are highly benfecial , like in digestion , gastric problems , etc .it has essential vutamins and minerals beneficial to the body.

We found huge load of it in our village “sandook”. Most probably made by our grand parents – Now we are using it in everything from cooking to fruits.. In cooking daal or vegetables, it tastes a bit like “charcoal” and is used half (quantity) of white salt.

Now whether or not it helps you/digestion system, it does on paper but in real life … I have no friggin’ idea.

For sprinkling on fruits like raw mango, papaya, guava etc and salad also in juice to give extra flavour

For normal home remedies like for gas problems with carom seeds and asafoetida

On salad & fruits

Churan and soft drinks.
Not for cooking,