As the tenor of a life begins to emerge from the manuscripts and I see a story unfold from one document to another, I have the sensation of making contact with the human condition as it was experienced by someone in another world, centuries away from mine. It may be an illusion, and I may get it wrong. I may sound like a romantic. But the archives, in all their concreteness, provide a corrective to romantic interpretations.That sense of an emerging narrative--that's what's so seductive about working in the archives, especially if it's a story that you haven't seen someone else tell. The problem is, of course, that not all stories are going to be of interest to anyone but you, which adds a third dimension to Notorious Ph.D.'s questions: Which parts are major, and which ones are minor? How can you tell which leads are worth pursuing because they'll actually be important, and which leads are just the means of satisfying your own curiosity about a particular idea? And, more importantly, is this a distinction that you should even be making as you're looking at materials?
Frankly, unless you're looking for something very, very specific, I don't think that you can make that distinction when you're in the midst of working with materials, although it's hard not to, given the time constraints involved in being at a research site. You can't know what's major and what's minor at that time, although you can know what's been published and what hasn't, which can tend to guide your search. If Author Y's love letters have been well mined for articles, you need to know those articles going in so that you don't "discover" a narrative that's already been written.
Also, the work you put into getting some information may be vastly disproportionate to the space it ultimately occupies in the finished work, but it may be very important nonetheless. In a recent biography that I read of Author X, for example, only a paragraph or so was devoted to one part of his life, yet I knew (because I knew the author of the biography, which took him many years to write ) that finding this information had involved painstaking research in half a dozen archives, just for a seemingly minor piece of information.
So what if this one small piece of information that you found in the archives proves that Author X really did read and respond to Author Y, or really was present in, say, a war zone even though generations of critics have said that that didn't happen? Some theorists might say "Who cares?" and that it's a minor point, given that queer theory, postcolonial theory, or whatever says that theory Z explains it anyway without the need for facts, and what are "facts" but an artificial construct based on hegemonic and ideologically driven narratives, blah blah blah, etc. But the thing is, if it's a point that no one has mentioned before, it deserves to be seen and heard, doesn't it?
I can see that this post is "casting about until a pattern emerges" and not getting there, so I'll finish with this: Part of what archival research is about is letting the narratives that are there in the documents, and the narratives that are not there but are implicit in the documents, teach you what narrative you ought to be constructing once you're away from the archive. So, in other words, you need to pursue those insights but also let them rest at the same time so that you can discern the patterns.