Just wonder if press releases really do work in terms of seo, marketing in general besides getting the word out?

Of course the paid ones may get picked up by larger syndication like NYTimes etc but they cost a lot and even so, is it worth doing them? The sales agents say I should do them every month for them to be effective but of course it costs something like $300 each time!

What about free press release sites? any good from the search engine's perspective and what other benefits?

Any insight to it is appreciated.