Owning my own car isn't all that convenient. I have to have it serviced. I have to refuel it. It's not always the ideal model for the task at hand. Every so often I have the hellish experience of buying another one. I have to juggle usage with other family members (or spend significantly more money for another vehicle that'll be less used).
Autonomous taxis would be more convenient than taxis driven by real people simply because you could afford to have a lot more of them on the road.
Even in rush hour, it would be common for an autonomous car to complete multiple trips so there's still a significant increase in utilization there. Also, sane road rules would give one-person micro-cars preferential treatment over space-wasting big cars.