When my mother is boiling or steaming food she uses a low flame. This way the food is cooked for a longer period of time . The cooked food is soft snd easy to digest. Most continental dishes are cooked in a low flame. When my mother is frying or makimg something which needs to be cooked to the core really fast she uses a high flame. The food gets cooked very quickly. Most pakoras and oily dishes which are deep fried are cooked in high heat flame