Many car rental companies will assign you a car before you arrive at the counter to pick it up – especially if you’re a member of their frequent renter programs.
They will normally base this allocation on the time that you’ve given when you rented the car, but if you’re arriving by air then this has the issue that your flight could be early or late, so your car may not be ready when you arrive (if your flight is early), or they might allocate you a car and then not have you arrive for potentially even hours for a very delayed flight.
By providing your flight information they can more intelligently allocate the cars – they can track the actual flight arrivals, and then allocate a car only when your flight lands. If your flight is late, they will not necessarily allocate you a car until hours after the time you had stated you were due to land.
For you, the benefit is that if your flight is delayed, they will know why you have not yet arrived to pickup your car. Rather than potentially canceling your reservation as a “no-show” when you haven’t arrived for several hours after the booking time, they will know why you are not there and keep the reservation. At some locations they may even choose to stay open past closing time based on the fact they know you are still on the way.
In the event that you end up (for example) changing flights and arriving earlier than the flight you specificity there’s still not issue – they will just assign as car when you arrive to pick it up.
So if your flight is delayed the car company know why you are late picking up the vehicle.
You are not being charged extra.
Credit:stackoverflow.com‘