Deciding how to shelve collections can be a very difficult decision. On one hand, we want to "save the time of the reader". On the other hand, we may actually be making titles more difficult to find by putting them where a library user may not think to look. I am ultimately opposed to treating GLBT and African American titles as special collections including labeling and assigning separate shelving locations.
It's true that shelving is a method of passive readers' advisory, but I think it's beneficial for librarians to examine their motives for separating fiction. GLBT titles are often the most frequently challenged books, admittedly usually children's and YA titles, but adult titles may be challenged because they may fall into the hands of a child. Moving "undesirable" titles to a separate collection is often a compromise when materials are challenged, as well as a method of keeping materials from their intended audience.
Separate shelving may have a chilling effect on reading. The American Library Association is opposed to labeling, thus presumably opposed to separately shelving, GLBT collections. Identifying books as GLBT "may prevent library users from accessing them for fear of being outed" (American library Association). Shelving African American collections separately may also keep readers away from checking out titles because they assume the books "aren't for them".
I question whether GLBT and African American fiction really separate genres, and I think it's reductive to ignore the diversity of GLBT and African American authors and shelve them together regardless of subject matter. N.K. Jemisin wrote an excellent take on this issue upon finding her science fiction/fantasy series shelved in the African American fiction section of a public library.
Joyce Saricks wrote in a 2006 Booklist article that sometimes we focus too much on genre and get caught up in how to classify a book that seemingly defies classification. This dilemma often is resolved by shelving materials where we think our users would look. (Saricks, 2006). What about Beverly Jenkins? Should she be with Romance or in African American fiction? Does James Baldwin go in the GLBT, African American, or classic section?
I think good cataloging and readers' advisory, including passive RA techniques like reading lists, social media posts, and finding aids are the best way to promote these collections.
The American Library Association. Open to all: serving the GLBT community in your library. http://www.ala.org/glbtrt/sites/ala.org.glbtrt/files/content/professionaltools/160309-glbtrt-open-to-all-toolkit-online.pdf
Saricks, J. (2006). Thinking outside the genre and Dewey boxes. Booklist. 1 March 2006.