The use case I heard was if for example the user clicks to load a view, which launches a background request, but then changes their mind and clicks to load a different view, which launches a different background request.

The user no longer cares about the original request. You could just discard the data when it arrives, but what if it's an expensive request for the client, or server, or both? You'd want a way to opt out of all that extra load on the system.