This is done to save building space, as is often the need due to the growing size of printed collections. Many libraries contain compact shelving in lieu of or in addition to off-site storage. It is also a common solution to space limitations due to the difficultly in securing funding for building expansions, and a solution to redesigning bookshelves with narrow aisles to be ADA-compliant.
The increased weight per area of compact shelving often necessitates that it be kept in the basement. Plans for compact shelving should be included in the architectural planning stages of a library building.
Some compact shelving units use a manual crank to move the shelves back and forth. Others have motorized controls, with weight and other physical sensors in place to avoid injuries. For this reason compact shelving may be closed to users.
High-use items should not be put in compact shelving, as it cuts down on the browsability of such materials and they are more time-consuming to retrieve. Users unfamiliar with operating compact shelving units may also be deterred from retrieving items kept there. Low-use items such as duplicate copies, materials available in another format such as microform or online, and other likely weeding candidates are best kept in compact shelving.
As with all items stored in special library locations, materials in compact shelving are cataloged with distinct location codes and physically marked as such so that they are shelved properly. However users not noticing the location codes in the catalog record may unsuccessfully search for them in the general stacks, and library staff can mistakenly return the items to part of the general collection.