The first bodybuilding coach I know of to make use of this technique was Vince Gironda. Vince generally advocated slowing down movements and performing them very strictly. Then he’d also have his students train in a more explosive manner for a period of time.
Each champion I trained with had different approaches to the tempo of a rep. Danny Padilla for example liked to keep his tempo fairly quick while still under control. Most of his exercises were performed for 12 repetitions in a 1½ second up 1½ down tempo with zero rest at the top or bottom of a movement.
On the other hand, when I trained with Mike and Ray Mentzer, they advocated performing reps with a 2 second up and 4 seconds or more down rep speed. They preferred to keep their reps low in the 4 to 6 reps per set range. They also rested 1-2 seconds at the top and bottom of each rep.
According to Charles Poliquin, German and Scandinavian strength coaches emphasize ‘super-slow’ style of training for athletes who need to increase muscle mass. Slower tempo increases muscle tension. The more tension your muscles create, the greater the stimulus for growth in muscle mass.
Let your ego take a back seat because you’ll have to lower your training poundages to compensate for the lack of momentum, but the added muscle mass you’ll gain quickly will be worth the ego check.
As with all good things, your body can and will adapt to the slower training tempo so cycle this with periods of faster tempo for best results.