that tab shows the cars you have set to online mode. if a car is set to online mode people on your friends list can just see the vehicle. you can't use online cars for online racing, and i dont even think you can use them in b/a spec. you must switch it off online mode.
its just a way of showing off your prized cars that you don't use often i guess? you can also set your BOB to online as well to share his stats with your friends.
PD might make use of this function as a share type thing, but as of now its just a way of showing off.
someone please correct me if my understanding is flawed on this subject
Nate