Ducted units come in handy where there just might not be enough room for a wall mount or floor ceiling unit. Slim or Concealed Ducted units are engineered to be hidden behind a false wall, in a closet, or in an attic and work in a similar fashion to a central system in that they do have some minimal duct runs. The benefits of using a ducted unit are higher efficiency that a central system, and the ability to condition several rooms that might be too small for a separate, single indoor unit.