Keep previously loaded serialized objects in memory

As previously mentioned, once a serialized object has been loaded into memory, then it remains there and can be copied if we need it again later, such as instantiating more copies of a Prefab. We can free this data later with explicit calls to Resources.Unload(), which will release the memory space to be reused later. But, if we have a lot of surplus memory in the application's budget, then we could choose to keep this data in memory, which would reduce the need to reload it again from disk later. This naturally consumes a lot of memory with more and more serialized data, making it a risky strategy for memory management, and so we should only do this when necessary.