my $a = "abcdefghijklmnopqrstuvwxyz";

use Benchmark;
timethese(1000000, {
  's1' => sub { s1($a, 5) },
  's2' => sub { s2($a, 5) },
});

sub s1 {
  my $a = $_[0];
  $a =~ s/^.{$_[1]}//;
  return $a;
}

sub s2 { 
  substr($_[0], $_[1]);
}

Results:
        s1:  8 wallclock secs ( 7.95 usr +  0.09 sys =  8.04 CPU)
        s2:  2 wallclock secs ( 2.54 usr +  0.01 sys =  2.55 CPU)
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