[noogle]

1. Flexibility. For a rental car you need to plan ahead, pick it up on time and return it on time. Traffic jam delaying you? too bad. You now pay a surcharge.

2. Cost: the rental cost is actually only a small portion of the cost. Extra insurance and other fees end up more than the rent itself.

Your car will depreciate regardless of that road-trip, just by virtue of time passing. Rental companies won't subsidize the wear and tear for you, so you have to pay that anyway.