My only point was regarding when you simply want to return a false value to indicate a subroutine failure. Consider the following contrived example where we only want to process strings beginning with a particular pattern:

#!/usr/bin/perl -w
use strict;
my @patterns = (qr/^foo/, qr/^qux/);
my @strings  = ('foo bar', 'bar bar', 'qux bar');
my @stuff;
foreach my $string (@strings){
    if(@stuff = dice_it($string)){
        print "Processing: $string\n";
        process_stuff(@stuff);
    }
}

sub dice_it {
    my $string = shift;
    foreach my $pat (@patterns) {
        return split //, $string if $string =~ /$pat/;
    }
    return undef;
}

sub process_stuff {
    foreach (@_) {
        print "<$_>";
    }
    print "\n";
}
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I'm not suggesting this a terribly common problem (or that the above is a good way to approach this particular example). I just wanted to point out that returning 'undef' as a failure mode isn't always appropriate -- and people who do so may forget that an array containing one undefined element still evaluates to true so they may bang their head for a while before they realize why they are processing the string 'bar bar' and getting a warning. Changing the last line of dice_it() to just a bare 'return' statement alleviates the problem because it returns the 'right' thing depending on context.