FSD Reduced Stopped Distance

When it's the last car in a jam, FSD should definitely keep plenty of distance so that, if you're rear-ended, you don't get pushed into the preceding cars. Ideally, FSD might even decide to move forward at the last moment to avoid being rear-ended in the first place (if it judges that this would give sufficient extra distance needed for the other car not to hit you).

However, once you're actually in a jam with other cars behind you, the distance should be reduced to a minimum as a courtesy to cars behind you who want to reach their exits.     It's stupid how much concrete is wasted by cars keeping way too much distance and keeping cars behind them from being able to finally leave the freeway. It's rude, really. It's why I always turn off autopilot when I'm in a traffic jam. I can't stand how much distance it wastes.

Of course short following distances make it harder for cars to change lanes, but FSD can always let cars in if they signal a lane change.

Agreed regarding danger of a rear-ender if you are last in line. Young Drivers recommends you stay back from the car in front until a car stops behind you, then close the gap.

I agree that "tighter packing of cars" is sometimes useful under some situations, such as turn lanes at popular intersections where the turn lane can sometimes be too short for the number of cars waiting to turn.  On the other hand, tightly packed cars (in any lane) can result in a multi-car accident that would have involved only two cars had the spacing between the cars been greater.