The default is 1. This is used in ObjectSpawnTemplate.con battle files to specify how many objects of the given type will spawn at an object's spawn point. That is, if set to 2, you could drive a vehicle off and another vehicle of the same type will spawn there, even though the first vehicle was not destroyed. In BF 1942 this value is set to 2 or 3 for airplanes or jeeps on some maps, e.g. Gazala. See NrOfObjectToSpawn if you want to limit the total overall number of objects to spawn.
Source and more details