When it comes to performing exercises, of course you want to do the movements correctly. Generally, most exercises should be performed slow to activate muscles properly. Now, if you are going for weight loss or endurance, the exercise can be performed a little faster, but keeping proper form. This will help get the heart rate up to help burn more calories. If you are going for strength, exercises should be performed more slowly, since the weight is also a lot heavier. If you are performing Lat pull downs for example, should you perform them fast or slow? Most of the time they should be performed slow. But, if your goal is weight loss, they may be performed slightly faster to get the heart rate up more.
Other exercises such as mountain climbers or burpees, should be performed at a high pace. These are better for weight loss and endurance because you are getting your heart rate up and helping burn more fat. The most important thing is, if you are going faster on an exercise, do the movement right. A lot of times people will perform movements fast and have bad form, because they are focused on the number of reps they are trying to get to. If you want better results while doing faster exercises, try to perform the movement correctly.