Margin funding provides extra cash for trading which you may not have at a particular point of time. It is used by many traders when they have an opportunity to make quick money but do not have enough cash needed for trading (margin) in the trading account. Its like a short term loan from the broker for trading purpose.
There are many use cases for margin funding. Here are few:
Confident on a tip/event and do not want to lose the opportunity because you don't have enough funds in the account.
T+2 days to arrange funds while buying stocks
Make most of Indra-day Market volatility and trade in Margin, Futures, and Options