a $ prototype forces scalar context

  DB<108> sub nopro  { print @_ }

  DB<109> sub pro ($) { print @_ }

  DB<110> @a=3..7
 => (3 .. 7)

  DB<111> nopro(@a)
34567
  DB<112> pro(@a)
5
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This is especially dangerous if your argument is another function call.

Giving a method a prototype other than ($;@) is at best misleading and will result in awfully ugly bugs if someone is assuming:

> $obj->method(...) and class::method($obj,...) (assuming $obj is of type class) are functionally identical

  DB<113> sub meth ($$) { print @_ }

  DB<114> main->meth(@a)
main34567
  DB<115> main::meth('main',@a)
main5
[download]

if you want a good self documentation, expand arguments to meaningful names:

sub meth {
  my ($self, $x_ax, $y_ax, $arr_ref, @opt) = @_;
}
[download]

I'm not sure what your understanding of "type" is in Perl's context.