These sources are good for finding grey literature. Grey literature are reports written by groups like think tanks, local advocacy groups, NGOs, IGOs, and governments. They are not published in the same way that other scholarly journals are so, importantly, they lack peer review. This means you should critically evaluate these reports and the groups publishing them to determine what perspectives and agendas they may be bringing to the topic. Grey literature can often be more current that other publication types that go through more formal publication channels.