Subsistent farming is the type that you make for yourself and your family. It is usually done on a small piece of land, and the produce from it can sort out your meals every now and then.
This farming is advisable because it reduces your food expenses.
I come from a farmer's family, we make money by selling out surplus produce. We sell rice, corn, lentils, and mustard. While I believe everyone should try subsistence farming, there is no harm in earning by selling surplus.