A Pool System (commonly known as Object Pooling) is a game technique where we pre-instantiate all the GameObjects beforehand and use them during gameplay, recycling each object from the Pool System. That way Unity doesn't need to use the Garbage Collector and therefore saves memory and CPU cycle time.

This demo shows a Unity package with a PoolSystem component able to recycle Prefabs during gameplay. Also, a custom editor will automatically instantiate in the Hierarchy window the desired number of Prefabs and make the whole process faster.

You can see the package at Unity Asset Store at http://u3d.as/1SKu