This mod has for goal to reproduce the universe of Half-Life, Opposing Force and Blue Shift (included by the way Black Mesa standalone and all HL Games close to the Black Mesa event). Play and see Half-Life from another angle of view to complete the background of this licence that changed the world.
So what is their application?
Actually no one, like in original Half-Life ahah, but in scripted mission you can make them useful to open specific doors for exemple