I always hear people say to use an amount of weight so you can meet your goal amount of reps in good form. On the other hand however, all the videos that I've been watching on YouTube show people taking big, massive weights and curling them with a slight swing of the arm or bending at the back a bit to use their feet and lower back to help lift the weight up. Yet they slow down during the negative to the point that they have almost full control over the weight.
Now one more point I feel I should point out before I conclude my question, according to Jeff Cavaliere of AthLEAN-X, the part of an exercise that is mostly responsible for fiber tears is the negative. He gives an example to explain this and says to think about our fibers like rubber bands. Not much happens when contracting a rubber band; however, stretching it out will eventually tear it. In essence what is happening during the negative portion of an exercise which then allows our fibers to grow back stronger than before.
With all that being said, I'm wondering if it is okay to waver from the correct form on the positives so long as there is full control on the negatives?