Think tank? Opinions on joining one

My boss has recently told me about his prior experience working at a think tank when he used to live in New York. He mentioned that these organizations help offer strategies and research in the fields of economics, government, and other sectors that could help the development in the U.S. and other countries. He told me liked the opportunity as he viewed it as giving back to a worthy cause while being able to have the resources for creative freedom in terms of what he could offer (ideas, implementation strategies, etc.).

I am curious if anyone could share their opinions about working at a think tank or any opinions you might have about it. I have just sent out my first application for a fellowship program they offer and I am curious if their is some factors I should take into account when considering joining one. Thanks in advance.