I made one pledge to myself in my never-ending quest to become a better saxophonist: I must play at least one thing in all 12 keys every day. The Saxtalk.com Colored Scales make this goal very easy for me to achieve: I just pick at least one scale every day, and I play it in all 12 keys.
I have been doing this now for several weeks, and I wanted to pass along one key take away: playing scales or etudes as very high speeds helps to improve your short-term memory. When you play a scale, song, or etude at high speeds, there is less room for error. Your brain knows this, so it commits pieces of a fast song to short term memory since it knows that you have less time to correct before you make a mistake that people (i.e. your audience) will recognize.
Practicing an etude, scale, or song at slow speeds builds your sound, intonation, and expressiveness. Practicing the same etudes, scales, and songs at fast speeds helps to build technique and working memory.
Playing at slow speeds and fast speeds are equal: you have to do BOTH to obtain a true mastery of your instrument. If you can play fast, but everything that you play is out of tune, no one will want top listen. I recommend that at least 1 or more times per week, you crank your metronome up to 200 beats per minute or more, and practice multiple repetitions of a scale, song, or etude in more than one key. Making a habit of doing this will improve your technique and your short-term working memory.