Consular legalization is required not only for POAs, but also for all kinds of documents in IP procedures. It’s a very important procedure, since all procedures depend on the validity of the POA and its attachments.
Legalization is made before the Consulate of the country where you need to use the POA. This is easy when your country has the required Consulate, however, it is possible that a certain country has very few consulates around the world, and you won’t find the one you need.
When you find this problem, there’s a procedure to legalize documents trough other Consulates.