To me, it genuinely makes a huge difference that I don’t have to manually press Ctrl+R for history search. Because 9 times out of 10, I accept a history suggestion from Fish where I did not think about whether it would be in my history.
This includes really mundane commands, like cd some/deeply/nested/path/. You would not believe, how often I want to cd into the same directory.
But I’ve also had it where I started typing a complicated docker run command and Fish suggests the exact command I want to write, because apparently I already ran that exact command months ago and simply forgot.
It still gives you basically no advantage compared to just making your terminal emulator launch
fishby default. And well, it does give you the major disadvantage that scripts without shebang will fail.