No it doesn't. This article is specifically about how you can use the Swift type system to prevent that from happening. You get a compile time guarantee that the result will either be data or error.

Actually, it puts the responsibility higher in the stack. The first error effectively terminates the computation, so subcomputations can ignore them and the caller can decide what to do with them.

One good thing about this is not having to push down anything to do with logging or reporting into subcomputations.

Not necessarily. The way that the enumerated type is declared, the associated types of the success and failure values are declared to be normal (not optional). This restricts nil from being passed in as the data or the error.