I play scales daily, but I don't spend more than ten minutes at a time on them, or more than 20 minutes total. The brain has to stay on for there to be improvement, and it is very easy to go into autopilot!When I say scales, I mean purely technical work, encompassing scales as such, arpeggi, octave work, independence exercises, etc. I find that I am able to identify "global" pianistic issues very quickly (occasional thumb tension in the LH, for example) this way. It is also an opportunity to work on velocity per se, unison, and thumb crossings. All of these things can be found in pieces, but I find that an extra 20 minutes per day working on them in isolation is beneficial (I have experienced considerable improvement).Best,Mike