You probably haven't spent a lot of time pondering what would happen if you lost your rental car keys.
I travel monthly on business. Until my trip to Arizona this month, I hadn't given car keys any thought. Probably I never would have if I hadn't changed my reservation from National to Dollar - something that I did because I was traveling with my 22 year old son. It turns out that car rental companies vary more than a little in their underage driver policies and prices. It also turns out that you have to factor in all kinds of other variables if, for example, you want to rent the car at one airport and return it to another. At best - if the company will do it at all between the two airports that you have in mind - this means an extra fee.