In theory, Sidecar is about sharing. Here’s how it’s supposed to work: You're headed downtown in your car, but before you leave you check your Sidecar app. A user a few blocks down is looking for a ride in the same direction. You swing by, pick her up, and drop her off. Everyone wins by sharing -- she gets to her destination, and you get to feel good that the gas you just burned went towards transporting more than one human being. (Plus, Sidecar suggests that she “donate” a little cash to you for your trouble.)
In practice, Sidecar seems to work something like a taxi. There's no meter, and in beta trials, the suggested donation for longer trips beat actual car services -- but it's not clear that the people giving rides are just average Joes who happen to be going someplace. Instead, this might be their side business. Sidecar screens all the drivers, and the one example of a driver that Wired offers is a laid-off bank employee who uses the service to supplement his income.