> It doesn't convey much. $scalar or @array, that's all.

You're vastly underinformed. It conveys the mode of access. It shows at one glance if the expression is singular or list or pairs.

                      … of an array   … of a hash
    the whole         @a              %h
    one particular    $a[0]           $h{foo}
    values slice      @a[5,3,7]       @h{qw(bar foo quux)}
    key/value pairs   %a[5,3,7]       %h{qw(bar foo quux)}