First of all Im talking about a single object(platform) that is created multiple times on the map, so you cannot add function to recreate them all in their exact position, even if possible it would take too long to add actions to create hundreds of objects each in their exact position.
Second of all I have tested it works, it optimizes, If I have hundred objects and then I add few hundred more by external layout the game slows, so opposite will definitely work.
Some games with too many collision objects or big maps will be able to remove unused objects offscreen and recreate them back in the same position when player returns to them.
For Example I have hundreds of Platforms made by the same object:
Right now there is a way to remove objects offscreen but they are not created back. And there is way to remove object by action, but it will remove all the objects in that object.