It is a tradition and I being from India know that this does work out. Understanding is not required. When they are married as time goes on they will know each other and start to understand each other. But the problem with love marriages in India is that many of them have end in divorces. Once they oppose their parents and go for love marriage and if there is any problem after the marriage none of the relatives and parents will go for the support of their son or daughter.
With arranged marriages if there is any dispute between the girl and boy the parents do interfere and sort out the problems. The big point to be noted is that with so many years in the arranged marriage scenario there was never a divorce. But with now in the name of understanding and love there is no understanding at all.