Why half sari function is celebrated?
It’s an ancient custom to celebrate a girl coming of age or reaching her first menstruation cycle. The celebration is grand with family showing their affluence and hospitality.
In short this ancient practice reason was to announce that the girl who is now moved on to be a woman is now eligible for marriage proposals. It is not essential that she will be married immediately however the process will begin from this function. Additionally everyone will get an opportunity to see the family, wealth, customs and hospitality.
In a modern day setup, it is just celebrated as a custom and not aiming to marry the girl particularly. However you will still see grand setup for the function which sometimes better than a normal wedding function in India.
Although slowly the numbers are decreasing it still remains a very popular custom in south India.