Usually I add an explicit exit statement to the end of the 'main' part of the code ..

I don't .. because I use braces for my 'mainline' code. Here's a recent script I wrote based on something I saw on Twitter:

#!/usr/bin/perl

use strict;
use warnings;

#  Base 24 question from https://twitter.com/pwnallthethings/status/13
+43590455511023621

my @digits = qw/B C D F G H J K M P Q R T V W X Y 2 3 4 6 7 8 9/;
my %digit_value;

my $string = 'FCKGW-RHQQ2-YXRKT-8TG6W-2B7Q8';

#  Convert a base 24 number to decimal. This is a group of five
#  numbers, like a Windows key.

{
    my $v = 0;
    foreach my $d ( @digits ) { 

        $digit_value{ $d } = $v++;
    }   

    my @units = split ( /-/, $string );
    foreach my $u ( @units ) { 

        my $value = decode ( $u );
        print "$u -> $value\n";
    }   
}

sub decode
{
    my ( $str ) = @_; 

    my $val = 0;
    my @chars = split ( //, $str );

    foreach my $c ( @chars ) { 

        $val *= 24; 
        $val += $digit_value{ $c };
    }   

    return $val;
}
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There's no exit required because the closing brace indicates "That's the end!" to Perl. I have seen code where the mainline is right up against the left margin -- I never code like that, because it obscures what's going on -- it's the same level as the use statements, so I don't know where the declarations end and the executable code starts.

And I don't put an exit anywhere, because that would indicate I was bailing out early, instead of allowing the syntax to naturally indicate where the end of the procedure is. To be clear, I'm *not* saying your way is wrong -- it's just not what I prefer. I like my way because it's clear and legible. For me, white space is my friend.