A long time ago, it was a way to carry around filehandles. Perl 5.8 (I think) allowed lexicals to hold filehandles, so this use died out.

Most useful thing I've found is to make a list of simple accessors in a class:

{
    my @ACCESSORS = qw{ foo bar baz };
    for my $slot (@ACCESSORS) {
        no strict 'refs';
        *$slot = sub {
            my ($self) = @_;
            $self->{$slot};
        };
    }
}
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But even this has tended to go away with meta-object systems like Moose (which do similar things under the hood).