- Input was received - Input was processed/stored correctly - Outcome is X
Doing everything in real time can reduce confidence and understanding. If everything takes like 5ms it feels weird, sometimes feels even like nothing happened, so people might submit again or feel the need to call and check or whatever.
It's deceptive in the sense that you are waiting maybe 500ms instead of 5ms. But it can be better UX in terms of communicating what's actually going on and having people feel comfortable with their understanding.
On the other hand, artificially slowing down something like closing an advertising modal - antipattern for sure.