ios-starter | Cookiecutter and XcodeGen template for our iOS apps

During initialization, your view controller adds a childAdded observer to a given Firebase database node. The passed in closure would still be called even after the view controller was long gone (i.e., deallocated). Firebase keeps a strong reference to it (and a weak reference to your view controller, by the way). This unnecessary calling might not be a major issue (yet!), but it's wrong nevertheless.

The deinit code prevents that from happening.

The deinitializer is called immediately before your view controller is deallocated. As such, it provides a nice place to remove that observer from the aforementioned database node. The observer (reference) is stored in the _refHandle property.

By the way, you could simplify your observer removing code to: