I have always wondered why certain instruments are in certain keys. For example, a tenor saxophone is in the key of Bb, which means that a C played on a tenor sax is in reality a Bb in concert pitch, where A=440 Hz. The result is that if a pianist and a saxophone are playing together, their music will be written in different keys. This always seemed unnecessarily complicated to me, why not just call a C a C?
I have learned the reason for this convention. Start with the saxophone family. The sopranino, alto and baritone saxophones are in the key of Eb, while the soprano, tenor and bass saxophones are in the key of Bb. By putting the different saxophones in the different keys, rather than naming the notes by their concert pitch, a saxophonist is able to play all members of the saxophone family, by standardizing the finger positions. The same finger position is a C, in the instruments key, for all of the instruments. I think that this is what Kriston was trying to explain to me last night, but you know beer. I don't really know why I am posting this, I just find it interesting.