Earlier this year when he was in Baltimore, Lukas held a masterclass with some of Manuel's students. When Lukas talked about slow practice, Manuel mentioned that Lukas used to tell him the speed at which he practiced was "glacial".
It has taken me a while to understand this slow practice thing, but I think I'm understanding it better, having seen some positive results lately.
I believe the point of slow practice, to the degree that Lukas mentions, is to:
1) know EXACTLY what motion(s) you need to practice
2) train until you obtain a degree of control of that motion that did not exist before, eliminating wasted motions
3) have that control firmly established until it is second nature
I've found that once it is second nature, speed comes naturally as it is just the same motion only less time in between.
I'm still struggling to incorporate this routinely into my practice as the desire to "play" overwhelms the desire to practice. On the one hand it is a lot easier and less stressful to concentrate on practicing because I'm not working the entire piece at once, but it is also stressful thinking that I'm NOT working the entire piece and it will take me forever to finish it.
I think the problem with amateurs like me, is that our technique is so lacking in so many areas, that if we took this approach literally, we would never finish a single piece. I believe these guys are advanced enough that the areas needing work is much smaller and they learn it much quicker due to their past experience with it. But I still think it has tremendous value for me and I hope to gradually incorporate more of it into my practice.