As someone whose lifestyle involves a good deal of formal and dressy cocktail events, I know a lot of people who use RTR. They do the one-time rentals, not the subscription. It always amazes me that it is touted as the budget friendly way to get a dress. I admittedly have a Shopping Problem when it comes to fancy dresses, but I am able to purchase them for equal to or often less than the prices of rentals from RTR. Ebay, consignment, and discount stores (TJ Maxx, etc.) allow me to find dresses in a similar price range, and I can wear them more than once. Also, there's no stress about whether it will fit or not come Ball day, even with the back up size RTR sends. And I can hem as necessary.
In other words, I can purchase for the same cost or less than renting, though admittedly it wouldn't typically be the same designer brands.