How much space do you need behind another vehicle stopped at a intersection?

In recent times some drivers have started to leave enormous gaps or space behind the other vehicles in front of them that are stopped at intersections.  Why would you do that?  How much room do you need? There actually very little reason to do this as all it achieves it to delay the flow of traffic through the lights when they do turn green.

There is some crazy theory that it enables vehicles to get through the intersection quicker because cars have more space in which to find more speed within the speed limit and therefore more cars can get through. IT DOESN’T WORK!!!

You only need to leave a safe space of 1 to 2 meters, anything greater than that is just wasting space and disallows others to progress through the intersection that would have. If you are stopped behind a 20 tonne truck on a hill you might want leave a bit more in case they roll back as they start off but most truck drivers will never roll back more than  a meter.

Also many intersections now have a left hand slip road with a give way sign that allows a driver turning left to bypass traffic waiting to go straight ahead. If the drivers leave excessive  space to the vehicles in front of them then a driver turning left may be blocked from doing so with only 2 or 3 vehicles waiting at the signals instead of 5 or 6.