There are some subtle differences:

1. Unless the declaration of some_subroutine was moved up, there would be a warning about an undefined subroutine. The assignment runs after the declaration (which happens on compile-time) and so no warning.
2. if the code were using anonymous subroutines as in

   my $coderef = sub {
       #...do something with @_...
       return ($value1, $value2);
   };
   [download]

   there would be no entry on the current package/namespace/stash. That makes a really private code.