Inside the isLocationEmpty function (CRM/Core/BAO/Location.php), there are several calls leading to potentially slow and definitely useless queries. Here are some examples:
$location->find( true ); [calls the query->] SELECT * FROM civicrm_location
$email->find( ); [calls the query->] SELECT * FROM civicrm_email
$address->find( true ) [calls the query->] SELECT * FROM civicrm_address
with no WHERE or ORDER BY clauses.
To give more context, I have a Drupal site where anonymous users can sign petitions, and where a contact is created with crm_create_contact if their email is new. This site has nearly 200,000 contacts, and sometimes these petitions undergo heavy loads. I started noticing the above queries popping up, and causing massive MySql slowdowns (as you might imagine with so many contacts). I'm attaching the relevant parts of a trace generated by the wonderful civicrm_error Drupal module, which I called manually in _query when one of the above queries was made.