$ perl -c -we'f()+123'
Useless use of addition (+) in void context at -e line 1.
-e syntax OK

##</code><code>##

$ perl -we'my $hr; $hr->{stuff}{foo}'
Useless use of hash element in void context at -e line 1.

##</code><code>##

$ perl -we'my $hr; $_ = \%{ $hr }; $_ = \%{ $_->{stuff} }; $_->{foo};'
Useless use of hash element in void context at -e line 1.

##</code><code>##

   ___________________ scalar context pad fetch. autovivifies
  /   ________________ deref
 |   /    ____________ scalar context hash fetch. autovivifies
 |  |    /     _______ deref
 |  |   |     /   ____ void context hash fetch. warns.
 |  |   |    |   /
|--|-|------|-|----|
$hr->{stuff}->{foo};

##</code><code>##

$hr->{stuff} //= {};