Speed: The Fast Lane To Pain

I was at the gym today working out and another member of the gym watched me do a set of one of my exercises and decided to help me out. He was an older man, slowly balding, but he was actually in good shape. He was a personal trainer.
  "I'm sorry," he said, "when I see some one doing something wrong I just have to tell them. Do you mind?"
  "No, not at all," I reply, stepping back from the bench to let him show me.
  He shows me the proper way to do the workout, which was some kind of tricep-pull-up with a dumb bell. There were a couple of subtle mistakes in my form and my speed was too fast. He told me that using to much speed potentially increases the risk of injury and "cheating," during your exercise (cheating, as in you're not isolating and working the specific muscle group correctly). I tell him that I do it as though I'd be doing it in real life situations, to which he said, "yes, well this will help you out during your real life situations, and it will make it a lot easier. It will also help you gain muscle faster too."
  I nodded. I finished my last set of the exercise and he watched me as I did it. Afterward, I looked up and said thanks. He was happy to see the change and continued his own work out routine.
During the rest of my workout and the bike ride home, I was thinking about his advice. After all, he was a personal trainer. I had been doing the same kind of work out for years and it has worked for me. Changing how I exercise is not too big of a deal, however, taking on new advice and discarding the old doesn't sit well with me.
  I had read a workout still that was made by a criminal serving time in the U.S.A. and it actually made a lot of sense, not just in the gym but outside as well. I also read about another trainer's regimen that he makes his clients use. The criminal said, "Do all your exercises quick and with little break time." (Maybe a minute break.) The trainer had almost the same idea, do all your exercises with little break time with a get-in, get-out mentality. The idea behind these workout mentalities is that with little break time, you give your muscles less time to cool down and result in injury. It also is the idea that strong muscles are made through continues use and work; you don't work hard for a little bit and take a 5 minute or 10 minute break in between.
  Control is a major concern when working out. Control your speed, form and safety of your exercises and you'll have a steady progression and improvement. Ultimately, I believe that is what the personal trainer was trying to say and I agree, although, I wasn't consciously practicing the element of control. After having done the same type of exercises or tasks sometimes you don't recognize that your form or technique get's sloppy. I'm glad that personal trainer pointed it out so I will know for next time!