For my dayjob, I work in an academic research library. There's about 90 full-time staffers in my building, which is one of many library buildings on a campus of 40,000 or more, in a Midwestern college town. There are 17-ish libraries total in our system on campus, and many more libraries outside our system. It's nothing compared to Harvard's hundred libraries, but on the other hand, Harvard has a lot of dups. (She says, with a straight face.) There are about 400ish? library employees, and 700 student workers, maybe more now.
My department is both a production unit and a knowledge-work unit. One of our functions is for interlibrary loan, which means we coordinate the lending and borrowing of books (and other things; we call these "returnables") and also the receipt and delivery of articles and chapters (non-returnables). Our department is responsible also for an on-campus document delivery service, which means if a faculty member can't make it to the library, or needs something scanned from our collection for a course, we scan it for them. We also have a fee-based information service, which serves folks without a library affiliation (like law firms doing research for a case, for example).
I have worked every lower level position in this unit, either full-time or as a longer-term back-up, but I've mostly been a supervisor. Currently, my job has a nebulous title: I'm the "processing supervisor." Since everything has a process, and there are many thing I'm not involved with (which of course have a process), you can see the nebulosity. In brief, I coordinate ILL book circulation, which is something much less simple than circulation of our own collection; I oversee the shipping department; I manage
ILL is something frequently ignored by librarians and library schools, which is one reason I hated the semester of library school I attended. I daily have to negotiate the preservation of books versus the access of patrons issue. I argue with shipping vendors constantly, have a ridiculous number of old Union List codes memorized (because they are the basis of the modern OCLC code list), know many arcane things about journal abbreviations, and have been to every library on campus many times. I spend a lot of my time interpreting policies and intentions for a wide audience, including my bosses and employees, as well as patrons.
Mostly, we facilitate academic research. Books come in, books come out like a tide; articles flow like a river. People get excited when we find rare or difficult stuff. SOME people. Others take us for granted, give us crappy citations and expect us to find their article, when there are actually some dozen journals with the title "Bulletin," and yes, the year something is published DOES matter. It's like working in a giant warehouse and being expected to find brake pads when someone told you they wanted a "a part of a car, nearish the tire" sometimes.
I don't worry about my job going away, as we have had major increases in some of our services over the past few years. Libraries make do with fewer dollars, and you may be able to get enough copies of articles on ILL to satisfy your patrons, for less money than it costs to get a subscription to said journal.