The reasion I had in mind is as follows:

process( text => 'this is some text' );
process( file => 'foo' );

sub process { my $text;
 if( defined $_{'text'} ) {
  $text = $_{'text'};
 } elsif( defined $_{'file'} ) {
  local $/;
  open IN, $_{'file'};
  $text = <IN>;
  close IN;
 } else { die "Usage"; }
 #proccess $text and return result
}
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It allows a gretaer amout of flexibility in the calling of your sub.