I'm not convinced. Most of the argument seems to be that redundant UX is bad UX: > But by archiving the email, the email disappears from the list, which already implies the action was successful. > In this example, the button already includes a confirmation so the toast is entirely unnecessary. I vehemently disagree with the idea that just because you're already communicating something one way it's bad UX to include…
I think the suggested improvement clarifies what he means: if you're worried that the UI element the user is interacting with doesn't fully convey what's happening, then improve that element rather than adding a second element that divides the user's attention and challenges them to read quickly and make the connection themselves. Communicate the failure of their interaction in the context of the element they interac…
Taking the archive example: yes, the disappearing message successfully indicates that something happened. But it doesn't tell you if the message was deleted or archived, and misclicks are common. The toast unambiguously communicates what happened in addition to saying that something happened.
Additionally, I stand by my argument that consistency is valuable. By all means have in-context feedback, but also pick a standard way that you always use to communicate completion of all actions. It makes it a lot easier to understand and eventually make use of the in-context feedback which may not be as intuitive as you think it is.