sub family_member {

    my @params = @_;

    my $brother = $params[0];
    my $sister  = $params[1];
    my $mother  = $params[2];
    my $father  = $params[3];

    print "$father\n";
}

# to tell who my father is, I'd have to:

family_member( undef, undef, undef, undef, 'Larry', );

# now, imagine if you could use a function like
# this instead:

family_member({ 
               father => 'Larry',
            });

# ...and even bundle your brothers together:

my @brothers = qw( Jeremy Josh );

family_member({
               father   => 'Larry',
               brothers => \@brothers,
             });

# now, in the above array-style example, what if you
# wanted to add an 'aunt' between 'brother' and 'sister'?
# Your API would be horribly broken, along with your
# current documentation. You'd forever be having your
# users moving around undefs to deal with your changes.
# With named refs, the only time your users feel a bite
# is if you change what happens to a pre-named param:

sub family_members(

    my $params = shift;

    my $brother = $params->{ brother };
    my $sister  = $params->{ sister };
    my $mother  = $params->{ mother };
    my $father  = $params->{ father };

    # add an aunt
    my $aunt    = $params->{ aunt };

    # how 'bout grandparents
    my $grandpa = $params->{ grandpa };

    if ( $father ) {
        return $father;
    }
    else {
        return "I don't have one\n";
    }
)

# then, you can throw at it what you want, and
# get back what you expect:

print family_member({ father => 'Larry' });

# ...or assign it:

my $father = family_member({ father => 'Larry' });