It also makes the calling code self-documenting. This is a large win for anyone dealing with the code including you when you come back to it a couple months later and can't remember which of the 6 args goes in the middle or what happens if you leave arg 2 out, etc, etc.

Maybe, maybe not. Sometimes, it's rather obvious what the arguments are. Sometimes, all the arguments play the same role. And sometimes, it would be just bloody annoying to use named parameters all the time. Do you really want to write:

    my $substr = substr(subject => $str, first_char => 5, length => 3,
+ replacement => "bar");
    my @parts = split(subject => $str, pattern => qr/foo/, max_parts =
+> 7, keep_trailing_empty_fields => 1);
[download]

? I'm not sure whether it's more readable. Or whether it's harder to remember that a negative third argument to split indicates trailing empty fields should be preserved than it is to remember the name of the flag.

Completely agree. Of course built-ins are special and functions unlike object constructors have a higher tolerance for inlining things because they never get examined/reused/reset by name.