"Additional Tracks" question

[user-removed]

Okay, I have a question. I just listened to the new Sigur Ros album for the umpteenth time since it came out last Tuesday. What to my surprise but one of my favorite tracks, "Rafstraumer" never came around. Upon looking at the tracklist I noticed that the song was there but listed as  not available. Further down I noticed that it WAS available as an "additional track". Now I've never really understood what these "additional tracks" are all about, why they're tacked on. I know that sometimes they don't transfer into playlists but that's no big deal for me. I do, however, have a problem with the disruption of continuity when playing an entire album start to finish. Don't you think that kind of throws a monkey wrench into something that bands and producers invest a lot of time in, namely the sequencing? Anyone can tell you that the mark of a good home made playlist is the ebb and flow of the sequencing. So what is the point of "additional tracks"? What puts a track in that category? Do they remain there for the duration? I mean, will "Rafstruamer" never be the seventh track on "Kveikur" again or is this just temporary? I certainly hope it's the latter...I mean, can you imagine what "Sgt. Pepper's Lonely Heart's Club Band" would be like sans "Within You Without You" smack dab in the middle of the album?