For example, certain calculations could profit from it if one distributes them on several CPUs. What else do you have the expensive gizmos for? Here is a simple, admittedly somewhat pointless example:

#!/usr/bin/env perl

use strict;
use warnings;
use Math::BigInt;
use Parallel::ForkManager;
use Time::HiRes qw ( time );
use feature qw(say);

my $sleep_period = shift;
my $processes = qx(sysctl -n hw.ncpu);

chomp $processes;

my $pm = Parallel::ForkManager->new($processes);

$pm->set_waitpid_blocking_sleep($sleep_period);

say qq(processes: $processes);

my $start = time;

for my $number ( 1 .. 50 ) {
    $pm->start($number) and next;
    my $factorial = Math::BigInt->bfac(2000) for 1 ... 10;
    $pm->finish(0);
}
$pm->wait_all_children;

say qq(fork: ), time - $start;
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See also this eight-year-old thread from which the example comes.