It is far more efficient to return a reference to a large string than to return the string itself. Here are my benchmarks:

sub Str {
  my $Str = q{
    # Here follows about 100K of ASCII data
  };
  $Str;
}
timethese(10000, {
  Str => q{ my $R = Str() }
});
Benchmark: timing 10000 iterations of Str...
       Str: 29 wallclock secs (28.64 usr +  0.01 sys = 28.65 CPU)
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sub Ref {
  my $Str = q{
    # Here follows the same 100K of ASCII data
  };
  \$Str;
}
timethese(10000, {
  Ref => q{ my $R = Ref() }
});
Benchmark: timing 10000 iterations of Ref...
       Ref:  9 wallclock secs (10.50 usr +  0.00 sys = 10.50 CPU)
[download]