The number of people and voracity that toasts are being defended in this thread is quite surprising given how terrible of a UI element they are. They don't exist anywhere in the document hierarchy so users have to mentally piece together what they're connected to, they carry no context, and they happen long (in computer time) after the action that that caused them.

Toasts are a solution to "I did something async and don't know how to design an actually good UI to convey that." And having a UI element for that is pretty darn useful because of how often that situation comes up. All of our default UI metaphors buttons/checkboxes/input boxes are all synchronous— either updating local state to be saved synchronously with a button or synchronously in real time (like setting a preference cookie). It's just that the web forced async-by-default on everyone without updating anything else.

If you show a user a checkbox it's absurd that such a thing can fail or not apply immediately, you're emulating a paper form, how does checking a box fail? Same with flipping a switch. Even if the light doesn't come on the switch is still flipped. None of these elements make sense to be backed by a request/response.

In the example in the article when the user changes one of their settings a save button appears, when you click it there's a progress bar or spinner, and when it finishes it says "Saved!" We figured this out in Windows 95. Quit trying to hide the form submission. The need for toasts is trying to tell you your abstraction is leaking.