How to instantiate Prefabs for an endless game?

Hello , i am wondering for the last two days what would be the best way to optimize instantiating in an endless game similar to Stack or Tower Bloxx where you would want to keep each instance active in the game till the end to be able to do the final panning for your entire building ? I am currently instantiating as needed during the spawn on a project but was wondering if there would be a better way (not pooling of course since you cannot predict how many objects are needed and are not disabling objects after they are in the scene).