I'm sure there will be a ton of residual effects from FSD. One off the top of my head being Emergency Services will be able to respond to emergencies faster because of minimized road congestion.
And? Does that matter if we have better capacity/congestion planning because all the cars are self driving. There's so much wasted time in traffic and excess congestion because humans are at the wheel creating chaotic traffic fluctuations by their driving.
Yes. That does matter, a lot. Look up induced demand. Also consider that full-self driving will likely mean more cars on the road that don't even have a person in them.
Traffic backups and delays aren't just created from people crashing, it's because when you take a a dozen tiny humans and you put each of them in mostly > 15foot long cars, you now have 12 people managing to take up over 180 feet of space.
Speeding up emergency services is a solved problem. You take a lane that is filled with single-occupant vehicles, and you dedicate that to efficient forms of transit, whether it be a high-speed bus lane or a bike lane. Emergency services will not only opt to use that the majority of the time, they will also be less likely to crash with another vehicle due to not needing to weave lane to lane.