Archival research hasn't always been considered really OK, not necessarily something film scholars should belittle themselves with. But there's something in archives for pretty much everybody. It's not only about the cult of the great artist, a comprehensive archive will have material of economic, cultural and industrial, as well as artistic, relevance. Letters between producers and financiers, between directors and censorship boards, between production companies and agents. Financial reports, salaries for actors and technicians, recording schedules, all of this things can help bring order and clarity to the history of cinema. It can also help answer many questions of authorship and influence, challenge some held notions and put a lot of conventional wisdom in perspective.
But there is no denying the fact that one of the biggest thrills in going through archives is the discovery of information about individuals, and their thoughts and comments, their behaviour and their struggles. Sometimes a particular letter might change your whole view of somebody. Background information might disappoint you, or it might enrich your experience of watching a particular film.
I cannot quote here from letters I've read, you'll just have to take my word for the potentials they possess. But students of film history and theory should at one point be introduced to the world of archives, and hopefully get the opportunity to visit one for a social call. In Scotland, there are for example the wonderful archives of Lindsay Anderson, John Grierson and Norman McLaren at University of Stirling. I was there last Thursday, having a wonderful time. I was mainly looking at the connections between Anderson and John Ford (since my love for Ford runs deep), but that was just the tip of the iceberg. I will go back soon. And there are many more archives out there, just waiting to be devoured.