It means that not only your loadout, vehicle and experience saved, but also any explored and cleared bandit camps, exploration locations, harbors, mapped anomaly fields and survivor hubs will keep it's status after mission restart! This works both for local and dedicated server. Since version 1.41 overall exploration progress is now also persistent.
To map anomaly field for other players you'll need to find it's middle, just remember to keep you gas mask on all the time - otherwise you won't last five minutes. This fields spread all around the map, sometimes covering major parts of towns and present extreme threat to any explorers. From now on, they are not just minor obstacles, but significant 'game-changers'.
