The fact is that it is common sense, nothing more to see cases like this; it’s not worth sacrificing technical move more weight because you’re not working really what matters. However, such errors are quite common. Of course there are times when you need to put a little more weight and reach muscular failure to achieve progress, but again, no point sacrificing technique to move more weight, if you do the wrong way.
And it makes sense, risk of injury aside, for the simple fact that you are not working you have to work. For example, to perform the bicep curl, to do so with less weight, good technique, and concentrate the most effort in the biceps and the other flexors, sure we raise much less weight, but on against, we are working more muscles that interests us.
No point in making an analytical exercise (elbow flexion in this example we talk about biceps curl) to the whole body movement. Likewise, we’ve known athletes who raised an enormous amount of kilos doing squats, but with good technique corrected and effort concentrating on the legs were not able to lift and half the weight.
Same with abs: some people are satisfied doing sets of 50 crunches fast. However, when performing the same exercise slowly, concentrating effort at all times in the abdomen, without compensation with the help of arms or neck, or are unable to reach half of repetitions, however, though less repetitions, are of higher quality.
In short, something we already know, but sometimes forget: is intense exercise and control effort that is put, not only by the weight lifted. And to end the bicep curl, an example of variation of this exercise can help prevent the momentum back.