Example: Suppose you book a car for say 10 days, you take it at 4PM of the first day, and you know you are going to return it at 9AM on the 10th day (e.g. because your plane lives at 11AM).
Question: Given that you pay per day AND there is no extra fee for returning the car early, is there any reason not to put the return time as late as possible, i.e. in this case at 4PM on the 10th day? (I.e. saying that you will return it at 4PM, when you know that you are going to do that at 9AM already.)
My point of view: As far as I see, you don't have anything to loose in this case, only a slight benefit (if something unforeseen happens, and you arrive several hours late, you may miss your flight, but at least you don't pay an extra fee for bringing back the car later).
I understand that this is a slight disadvantage for the rental company, because they could have already booked that car earlier for someone else. However, I think that's on them: if they make me pay the same amount for using the car a whole day, or just half a day, I may very well decide to pay for the whole day, and return it earlier. (I.e., from their POV there is no difference if I really needed the car longer in the beginning, and then for some reason, I did not need it anymore.)
Related but not duplicate question: Can I return a rental car early?
That question asks "what happens if you return the rental car early"? The conclusion is that one of the three things may happen:
A.) You end up paying a little less. B.) You pay exactly the same amount, as if you had returned it in the original time. C.) You have to pay more. (As far as I understood, this can happen only if you return the car at least a day earlier.)
So, in other words, my question is: given B.), what are the disadvantages of returning the car several hours, but less than a day too early?
EDIT: I know that sometimes you have to provide your flight data too, so suppose in this case you don't do that. (Although it would be an interesting question too, what would happen if you book you car later than the departure of your scheduled flight and the car rental company sees that? Would they allow you to do this?)