Manually adding delimiters instead of join()

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Why must you join() these values instead of just storing them with common separators?

$users{$username}"$password::$name::$email::$website::$start";
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This stores only the first form field/variable and forgets everything else. But if you join the variables, it works.

  my $data = join("::", $password, $name, $email, $website, $start);
  $users{$username} = $data;
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Can someone explain why you can't manually add your own delimiters in this particular line?