Practice Makes Permanent
Dieter: I am so free to quote from http://www.guitarnoise.com classical guitar lessons by Logan L. Gabriel. I believe this viewpoint can be transposed immediately to the way we study Go. The idea is of course open to discussion.
MYTH: Practice makes perfect.
FACT: Practice makes permanent. In the words Al Woods (Tiger's Dad), "Practice makes permanent, PERFECT PRACTICE makes perfect." The fact of the matter is that if you let mistakes work their into your playing you practice the mistakes not the proper material. You are now probably saying, "Well of course i'm going to make mistakes that's why I've got to practice!" Yes, you are going to make mistakes but they can be minimized. The way to minimize is to play slowly.
MYTH: In order to play fast I have to practice fast.
FACT: You need to be able to think while you play. Aaron Shearer, a famous classical guitar pedagogue was an advocate of "aim directed movement", which is having a clear understanding of where the fingers need to go before you move them there. Aim directed movement can only be accomplished by slow practice.
Application to Go
BlueWyvern: Two points. One, I'd imagine that is a big difference between amateurs and professionals. Amateurs have practiced a lot of bad habits and have to work on getting them out, whereas pros don't get bad habits to begun with, having rigourously trained from early. Two, I totally agree with playing slow at first. I find I absorb a concept and can play it a lot faster if I use it in slow games first as I am learning said concept. I'd also imagine that if you play a pile of fast games, you will have a harder time picking up your mistakes at first, but because of constant repetition, they can become permanent real fast. ...
WilliamNewman: But Go practice isn't just practice in execution, but also practice in noticing and understanding things. If you are trying to learn to track animals, find promising places to drill oil wells, or diagnose diseases, you should probably allocate some of your time to survey a large number of cases, not spend all your studying a small number of cases very carefully. And while hasty misunderstanding of a few of the numerous cases is not helpful, as far as I can see it doesn't impair your execution of plans in the same sense that mispracticing a bad habit in golf or guitar might impair your ability to do it right.