Rep speed is the rate at which you perform the eccentric, isometric, and concentric contraction of a given exercise. There are a few considerations we want to go over before determining the rep speed.
9 times out of 10 we will want to lower the weight, stabilize, and then raise the weight as fast as possible with good control and technique.
Good control & technique means that you will not bounce or drop any weight. We lower quickly, stabilize and push hard and fast. To be strong you have to be fast.
The reason for this is that the longer you are under tension the more energy you will be using. If you miss a set because you are moving too slow than that is a problem. You will be limiting your progress.
Before each set you should be doing a specific warm up and to get into rhythm. Each rep should take the same amount of time to complete. However do make note that near the end of the set your muscle will be exhausted and naturally cause slow down.
The other times you will be performing a different rep speed is if you are using the time under tension intensity principal and moving the weight slowly. You would use this to build muscular endurance; in some cases maybe trigger hypertrophy.
Remember technique is paramount.
Dedicate & Succeed,