Isn't the point to go on the cheap?
The first time I got a rental car was while in college, our school started a Hertz Connect pilot which allowed students to rent the car for $8 an hour (including gas and insurance) or $64 for the day. What made this service compatible on a college campus was that the driver only had to be 18 or older. Typically, there are fees for drivers under the age of 25 and some companies do not rent out to drivers under 21. Both times I got a rental car, my school paid for it because it was for an organization activity. A lot of students that did own cars hardly drove it because our school was like a bubble, and so it was more cost effective to pay for a rental car the few times they needed it, rather than the cost of car ownership.
The first time I got a rental car after graduating was because I had a visitor and no car to show them around. At first I was totally flabbergasted at the price of the car rental because I'm under 25 so there was an additional $10 per day fee, which undoubtedly added up. Even after getting a car though, I still got rental cars on occasion. My car is 12 years old and struggles with driving uphill. On a trip to the Smokies (and again through the Smokies to Asheville), I was not going to put my car through that and potentially face mechanical problems sooner than necessary or worse, have the car break down on me during the trip. At least, if there was a problem with the car during the trip, I could call the rental company and they would bring another car. Sure, it would delay the trip but at least not ruin it. The cost for renting a car for the weekend would be far less than the cost of repairing a car (as I know all too well...).
I didn't think of this on my own though. I've known of people who drove their own cars for daily commutes to work and running local errands but renting a car anytime they made longer journeys. Part of that has to do with mileage, because no matter the age of the car, high mileage can shorten the lifespan of the car. So in the long term, rental cars can make sense even when you have a car of your own.
Plus, some Enterprise periodically runs a weekend special where it's only $9.99 per day (but a 100 mile per day limit and $0.20 per mile after that) and Hertz often has promotions such as waiving the under 25 driver fee and you can combine discounts. Hertz partners with AAA, some insurance companies, and probably other companies to offer discounts. The cheapest deals on rental cars that I've seen are on Hotwire, but to book you must be 25 years old. Bummer!