I do this pretty consistently - it avoids a small category of errors: assignment to the wrong variable is less common when there are fewer variables! But I have to agree that it's unusual. I'm always willing to forego this if the team objects to it because I think the advantage is slight.

I'm therefore slightly in favour of the val/var option over "final var" as the former might encourage the immutable by default approach since it requires less typing. I would guess the view would split pretty much exactly like that between those who do and don't currently use final locals by default. Rich bike-shedding lies ahead :)