Long run is just a form of aerobic training just like tempo work or threshold work. 800m runners should definitely do some form of aerobic training as it will help for sure with the event but it doesn't need to be a long run.
If you choose to do them or not its all about how much benefit you get from them vs recovery time. Plenty of guys now doing double threshold have scrapped long runs as they believe that replacing it with more threshold work provides more benefit and less time to recover from.
I believe the greatest benefit of long runs is the injury resistance they provide. Extra stress on the joints doesn't lead to injury. Too much stress does but extra stress leads to adaptation and more injury resistant