This option is used when we want to allow employees' to take more leave than the available leave in their account. Let's take the example of Pragya. She has only three leave of type Legal leave available in her account. When she applies for the leave, she can get the number of leave available for each type of leave:
She is going to apply for four days of leave even though she has only three 3 days available. When she tries to save the leave request, she will get a warning message as shown here:
If we would like to allow her to take more than her available leaves, the Allow to Override Limit field should be selected on Leave Type as Legal leave 2017:
As soon as Legal leave 2017 is marked as Allow to Override Limit, it will not display the available number of leave at the time of the leave request: