Expense? Just hiring a car would not be much more expense but would require more logistics, as you would have to manage scheduling and calling cars. To get a dedicated driver, or team of drivers (to cover 24 hours) and vehicle would be significantly more expensive than a couple extra vehicles. Plus handling the logistics of setting them up to be ready and waiting for you each time you travel would be something else to manage, or would be something to pay a personal assistant to manage. Plus you could still use car services as needed whenever you didn’t want to drive.

Unless you had reached a level where you were having almost everything in your life managed by assistants, and you were the type of person that wanted to give up all that control, then have “your car” ready to go whichever house you were at would be the lower mental overhead solution.