On observing the flame i discussed with my mother
the reasons are:
# Using low flame the fuel consumption(LPG) is very less,
using high flame consumes all the fuel fast.
#Keeping the flame controlled and low gives good taste to the food,because
the food gets overcooked and spoils it.
#using high flame is also dangerous.
#Using also reduces the amount in monthly bill for the gas (LPG)