It doesn't convey much. $scalar or @array, that's all. An array is always an array of scalars. Scalar can be almost anything: any kind of number, a string, a reference (often a reference to... an array or a hash, since you can't have arrays of arrays or array of hashes, only arrays of scalars).
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)}It's useful when you have a healthy mix of arrays and scalars scattered throughout your code. Static typing would be better, but $ and @ are better than tracking the information manually.