Open access makes sense for faculty who'd rather spend their time teaching. Even teaching faculty need to publish, and the more people who read your research, the better - but who's got the time to maintain a website of their publications? Heck, I'm a regular blogger and my publications list is out of date! With open access, you don't have to; if your institution offers personal researcher pages as a feature of their institutional repository, you automatically have an online portfolio of your publications. If your institution has an open access policy, that portfolio also makes those pieces available.
It may lead to your work being picked up by a new audience. "One of the things we've found is that new audiences are constantly revealing themselves to us," the repository manager of Cal Poly said in 2009, "and that's been the most surprising piece." (From Jean-Gabriel Bankier and Courtney Smith's paper on Repository Collection Policies [pdf].)
It's also something that can benefit your students, who can also often place their work (essays, dissertations, presentations, etc) in the repositories of their colleges and universities as well. If those repositories are open access, the students have an instant public portfolio for their scholarly work, which can lead to fascinating conversations with future teachers and employers. In other words, it's the academic equivalent to our usual argument for getting students involved in open source projects; open source gives you a portfolio of outputs of practice, whereas open access gives you a portfolio of outputs of scholarship.
Yes, grad schools can usually access published papers already, but that's a tiny fraction of a student's work; how many undergraduates have published papers? Even those who do will likely have a lot more good work that is not published anywhere (for instance, an undergraduate thesis), and plenty of students will want to show their portfolios to prospective industry employers, who mostly need open access to see any of this at all.
(This is, by the way, one way some faculty get into open access and institutional repositories themselves -- they nudge their students to put things into their school's repository, then go "wait, I could do that too.")
And this isn't just about big research schools. Jonathan Miller, the library director for Rollins College, writes about OA for liberal arts colleges.
Colleagues are surprised because they assume OA is an issue for researchers and the large universities that employ the majority of them. I argue that OA is not just the concern of research universities. In fact, it might be even more relevant for smaller colleges than for larger schools.
Rollins is a largely undergraduate, teaching intensive school with a liberal arts curriculum. This means that, at least in one sense, we need broad not deep access to information. We are net information consumers, rather than net producers. The subscription model of collecting a relatively small number of periodical titles “just in case,” doesn’t make much business sense for a school like us. What we really need is “just in time” access to a broad array of information resources, none of which will be used particularly heavily... the librarians are the faculty and students’ guides and partners in a larger, richer, but more complicated information environment.
If you care about teaching, you should care about open access. If you're curious and wondering where to learn more, here are the best resources that I've found.