The training weight
Most weightlifting programs rely at least partially on percentages to determine the weights used in training on various days. There is absolutely nothing wrong with this, but I believe that for many athletes, especially those at the level of novice or advanced, percentages should not be the last word in choosing the weight to train with.
It is typical for a novice to be able to max out with say a 70kilo snatch, which is ugly and all over the platform, but still make the lift. This same person might not be able to do 60 kilos for several sets or reps with consistently good form. 60 kilos is about 85% of 70, and it would not be atypical for a training program to call for several doubles to be done at 85%. Practicing with a weight like 60kg which would ensure rep after rep of bad form would not be the best choice for this person. I believe that if 35kilos is the most they can show consistently good technique with… then that should be the main training weight even though it is only 50% of max! Of course, the lifter should continually attempt to raise the weight at which he or she can show good form, and there will be periodic attempts with higher weights and even attempts with new maximums even if they are ugly. But there should always be more “perfect” lifts done than ugly ones, no matter how low the weight needs to be.
An advanced lifter is at the other end of the spectrum. Let me use as an example Caleb Ward, who has the most consistent technique of any lifter I have ever worked with. Caleb has as a best snatch 127kg. 85% for Caleb would be 108kg. 108kg for Caleb is so light that I really doubt there is any training effect whatsoever at that weight. Even on his light days he works to 110 or 115kg on the snatch. Caleb has been lifting for 5 years, is in great shape, very consistent, and doing anything up to and including 90% is about as challenging as getting out of bed in the morning. In training the snatch, Caleb works quite consistently and regularly with 120kilos, or about 95% of his max. Holding his training weight down because he is only supposed to hit a certain percentage would undoubtedly decrease the training effect of his workouts.
Percentages are good guidelines, especially for average lifters who are neither novices or advanced. However, they shouldnt be followed blindly.