The asterisk is such an ugly mark. It generally means there is an exception, a footnote that must be taken into consideration. On a CD, it is an indication that a particular song or track wasn't part of the original release. To some fans, this is no big deal; to purists, it is a blemish on an otherwise perfect album.
The bonus track is a feature of older music; back when vinyl records were the format of choice for most music. Because the size of the LP allowed for a maximum of approximately 22 minutes per side, artists were limited as to how much they could fit onto a particular album. This led to singles and the infamous B-sides, songs that the artists or record companies felt just didn't fit the album, but still deserved to be released and heard by the mainstream audience. Now that CDs allow much more room for "additional" songs, many albums are being re-released with the non-LP singles included. But is this fair to the vision of the artists?
In the early days of Rock, record executives sliced and diced albums with little regard to the artist's wish. This is why by 1966 the Beatles released 11 albums in America and only 8 in Britain. It is also why several Rolling Stones songs exist on two separate albums. The Beatles' release of Sgt. Pepper changed that, insomuch as the "concept" album determined that these certain songs composed of this album, neither to be added to nor reduced. Since then, most albums were released the same everywhere; the American version of an album was the same as the British version which was the same as the Japanese version, and so on.
When the CD format became mainstream, CD albums were initially released with the same content as their vinyl counterpart. However, as record executives and consumers alike became aware of the CD's capacity to store more music, record companies began releasing "updated" versions of CDs, and thus the "bonus track" was born.
Yet the question remains, is the bonus material really a bonus? It depends on the material and the artist.
Paul McCartney's 1973 release, Band on the Run, is an excellent album on its own. Released on CD initially by itself, a later re-release added some bonus tracks, including McCartney's theme to the James Bond movie "Live and Let Die." "Live and Let Die" was released as a single only (though it is included in his greatest hits packages), so fans looking to have both "Live and Let Die" and its B-side "I Lie Around" on CD may have lost them if not for the re-release. Yet with an artist like McCartney, who had so many singles released, it would have been better for his record company to gather all the singles and B-sides and release a whole new CD. This is, after all, what they did with McCartney's former band, resulting in the Beatles Past Master CDs, volumes one and two.
The other side to this is the original Jeff Beck Group, which released only two albums before splitting up. Had Beck-Ola not been re-released with additional tracks, Rod Stewart's excellent "Throw Down a Line" may have been permanently lost. However, Led Zeppelin's "Hey Hey, What Can I Do" was released as a single only, and did not reappear on CD until they released their box set in 1990. Led Zeppelin maintained the integrity of their original releases, yet still found a way to preserve their "lost track" on a new format.
Singles, B-sides, and unreleased songs are one form "bonus track," and whether or not their addition enhances or mars an album's integrity or the artists' vision is subject for debate; some "additional" songs can actually expand the listening experience, while others feel tacked on, as a marketing ploy to make fans buy two versions of the same CD. The other version of the bonus track, the alternate take, the "live" version, or the demo take" is an obvious abomination of the artists' intent.
Alternate takes and demos are interesting; they can be quite different from the well-known versions and even show how a song evolved. Though listeners may disagree, there is usually a reason alternative take was not used, and often it's the artists themselves who feel the alternative take was not as good as the released version. Fans generally love alternative takes, mainly because it's a way to get more of a favorite band. The Beatles did it right by releasing the Anthology collection. Those who wanted a fascinating look at the Beatles' process of work got to hear very different versions of classics and good insight as to why some of the unreleased material was unreleased. Taking on demos and outtakes on Revolver or Sgt. Pepper would ruin the enjoyment of the original finished product.
However, there are exceptions. In 1968, the Byrds released Sweetheart of the Rodeo, an album most people regard as the birth of Country Rock. The Byrds transformation from folk to country was facilitated by new member Gram Parsons who was to be featured on lead vocals for many of the tracks. Because of contractual obligations to his old label, Parsons was not allowed to sing lead, so many of the tracks were re-recorded with Roger McGuinn singing Parson's parts. When Sweetheart was re-released on CD, listeners got to hear Parsons' versions for the first time, as bonus tracks. This is a case where the artists' intent wasn't in the original release.
Live versions belong on live albums. You could even make a "best of" live album if you want, but don't add live performances to studio albums; they just don't go together.
My feelings on bonus tracks extend beyond the rock world. When given the choice between a classic jazz album featuring "bonus material" of alternate takes or a cheaper version that is the same as the album released in 1953, I generally go for the original.
I don't like asterisks; they're such ugly things.