They're not completely useless, but I do find that I don't seem to get much benefit from them.
For example, I needed to rent two cars on a trip last year. The first car I was able to rent through Air Miles, but I had to pay the taxes and any fees beyond the base price myself so it didn't feel like much of a deal. The second car required more Air Miles than I had, so I had to pay for the whole thing myself, I couldn't do part on Air Miles and part cash.
I ended up renting the second car through Costco and felt like I got a better deal overall than I did with the first car.
Maybe rental cars aren't the best way to use them.
For example, I needed to rent two cars on a trip last year. The first car I was able to rent through Air Miles, but I had to pay the taxes and any fees beyond the base price myself so it didn't feel like much of a deal. The second car required more Air Miles than I had, so I had to pay for the whole thing myself, I couldn't do part on Air Miles and part cash.
I ended up renting the second car through Costco and felt like I got a better deal overall than I did with the first car.
Maybe rental cars aren't the best way to use them.