Embedded librarians are integrated information experts that offer more direct research assistance to groups of faculty and students than the typical one-shot instruction session, often over the course of an entire semester.
While librarians can embed in face-to-face classes, they are increasingly in demand withinin virtual environments in order to support online classes, hybrid classes, and face-to-face classes that include an online support component.
That depends on what kind of presence you want to have.
Micro Presence - librarians usually work one-on-one with a faculty member with whom they already have a professional relationship. This is often seen as a more maintenance-intense approach because librarians shape their involvement to fit the needs of the class. Time commitments for this experience can range from a medium time commitment (ie, multiple asynchronous discussion activities) to a high time commitment (ie, multiple synchronous virtual presentations with weekly virtual office hours, graded assignments etc.).
Macro Presence - librarians generate tutorials and activities that can be used across many course groups, enabling a "drop in" component for online courses that requires a lower time commitment than the micro level. More students are served by the embedded library services this way, and the level of personal interaction between the librarian and the student is reduced.
Paraphrased from a white paper by Laura Wright and Ginger Williams, 2011. See Recommended Reading tab for more information.
And special thanks to Angela Colmenares of Sam Houston State University for the inspiration!