"In general" is misleading.

In the particular case where you've no variables in the string, sure, maybe, but it's not an interesting use case.

#!/usr/bin/perl
use strict;
use warnings;
use Benchmark ('cmpthese');
my $dqv = 0;
my $sqv = 0;

cmpthese(1000000, {
                 double => \&dq,
                 single => \&sq,
                });

sub dq {
  $dqv++;
  my $str = "see $dqv run                                             
+                                        and $dqv";
}

sub sq {
  $sqv++;
  my $str = 'see '.$dqv.' run                                         
+                                            and '.$dqv;
}
[download]

            Rate double single
double  943396/s     --   -37%
single 1492537/s    58%     --
[download]

"In general" is misleading.

In general, concatenation/single/double quoting, is not what programs spend most/all of their time doing -- its not the bottleneck -- its not important -- its not misleading