Several musicians are in the habit of training by transposing, often in all twelve keys, the harmonic progressions of the songs they choose to include in their repertoire. On the one hand, this kind of training allows the musician to progressively attain the capability to improvise "at first sight" on a significant number of traditional jazz compositions (regardless of the key, and this skill is surely useful when one plays with a singer!). On the other hand, in my opinion, the musician who is in the habit of following such a training runs the risk of becoming "simply" skillful: he/she will probably end up with playing the same "sentences", completely ignoring the genuine "spirit", as it were, of the particular composition (in other terms, without conveying any authentic message). Is it worth it? Maybe, the answer lays in the difference between a "simple" musician and an artist...