Memory Management
If heap memory were infinite, we could create all the objects we needed and have them exist for the entire run of the application. But an application gets only so much heap memory, and memory on an iOS device is especially limited. So it is important to destroy objects that are no longer needed to free up and reuse heap memory. On the other hand, it is critical not to destroy objects that are still needed.
The idea of object ownership helps us determine whether an object should be destroyed.
An object with no owners should be destroyed. An ownerless object cannot be sent messages and is isolated and useless to the application. Keeping it around wastes precious memory. This is called a memory leak.
An object with at least ...
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