Virtual objects F5 should be place everywhere on the map, where certain prototypes (vehicles, persons, animals, ships etc.) have restricted access. Every movable prototype has terrain settings which defines, on which areas the prototype can move - even movement speed on the terrain can be set in the properties (see '..\Specs\terrain.xml'). You should distinguish between land and water in each case.
If you activate the checkbox 'Leave tracks' vehicles and persons can leave tracks on the floor in the marked area. The option 'Snow effects' is needed for areas, where the rescue dog should leave snow tracks and effects.
You should never place virtual objects overall the completely map. Always place them on the floor and optimize the areas by separating the objects in smaller ones.