Agreed. Combining the ability to call a subroute to do your bidding and back references makes for some very handy abilities.
For example:
Say I have a string:

"The %NOUN% can jump very %ADVERB%"

And say I have hash:

%wordBank = (
NOUN => "kangaroo",
ADVERB => "far",
)
[download]

I wanted to replace what is in the string with what is in the hash, so originally, I iterated through the hash and did a replace on the string as I found each hash key. This is terribly inefficient, so I reworked it to find items delimited by %..% in the string, and used the delimited keyword to directly call the value from the hash. This save me a lot of time, especially when %wordBank is very large.

#!/usr/bin/perl -w
  use strict;
  sub safeReplace {
    my($hashkey,%hash) = @_;
    my $hash = \%hash;  
    my $retval = '';
    if (defined($hash{$hashkey})) {
      $retval = $hash{$hashkey};
    }  else {
      $retval = "\%$hashkey\%";
    }
    return $retval;
  }

  sub preProcessStr {
    my($string,%options) = @_;
    $string =~ s/%(.+?)%/safeReplace($1,%options)/ge;
    return $string;
  }
  
  my  %options = (
              ARG1 => "test",
              ARG2 => "123...",
             );
  my $string = 'Hello %ARG1%, counting down %ARG2% .. %NOT%';
  
  $string = preProcessStr($string,%options);
  print "$string\n"
[download]