I see people doing half reps with improper form and really heavy weight. Is that optimal?

Today specifically, this guy started doing lateral raises with the 35s. Only, he only brought the weight up to about his lowest rib, and was using his whole body. He got maybe 5 reps this way, and only did two sets. When I do lateral raises, I do light weight(im a beginner so rn im doing 17.5 LB on each arm), and stand still and sweep the weights up until even with my shoulders. I go to failure, normally 6-8 reps. Is one of these inherently better, or is it always better to use proper form? I would assume if nothing else, using heavier weights would lead to higher injury risk, right?