Negative reps (lowering dumbbell) is often overlooked in weight lifting. I see people trying to lift fast but have bad form. Negatives are where real strength and muscle is built. See: Dorian Yates.
I think this started when crossfit style programs gained popularity. It's all about pumping out as many reps as possible in the shortest amount of time.
While that's good for elite athletes who compete in the sport. For the general gym-goer it's just asking for injuries to happen.
Before anybody undergoes any major lifestyle change, for the love of fuck, listen to the warnings about checking with your doctor, you might be glad you did.