If rides could show up instantly, it would be more efficient to just get a new 'ride' for every leg of your trip. But Phoenix is spread out, and you can't always count on a car being nearby.

It typically took me 7 minutes to get to a pickup address, which included a minute to plug the address into my navigation software (the taxi company I used to drive for now has a phone app that automagically directs the driver to the pickup address, just like the upstarts' system). The mother of a friend of mine has taken to using "Lifts" when she needs to go someplace where she'd rather not have to park. I explained that the driver she was getting might not actually be just around the corner.