Overdraft (OD) facility is a facility that allows you to draw more money than what is available in your account. It's like an extended line of credit. For example: if the bank grants you OD of 50k, then you can use up to 50k in credit. You have to pay the bank interest on the amount of OD you have used. If you use OD of 10k then you pay interest on the 10k. I think the OD interest is BLR + 2%.

Take the OD facility if you feel you need some credit on hand to use.

Be aware that some banks charge a commitment fee for the OD, meaning even if you don't use the OD at all you still have to pay a fee for having it available.