x ([: u v) y expands to u (x v y), but so does x u@:v y. @: strictly supersedes [: in Special Codes. Is there any reason to use [: over @:?
Some people prefer ([: f g) to f@:g for readability, perhaps because it is more spread out, although f @: g accomplishes the same spacing without parentheses.
I am pretty sure that I have seen cases where it made a difference to the outcome, but I can't remember them now. Perhaps others will be able to come up with examples where they differ.