Jump setting is a great setter's tool, and it creates many advantages.
First, it speeds up your offense because you can reach the ball sooner.
Second, it often makes it easier to set quickly or shoots because you're closer to the height of your attacker as she jumps in her approach.
Thirdly, it help you fool your opponents into thinking you're going to attack.
When they put a blocker on you, it's one less blocker for your hitter to worry about. Some setters like to jump set to the outside because most setters jump only when they're going to set the middle. It's important that setters learn to set every set both from the ground and from a jump set. When you jump set, make sure your feet are in position first, then you have to be under the ball to make an accurate jump set. Use the same body and hand positioning as you'd use on a set from the ground. Set the ball when you reach the peak of your jump.
You need to practice, practice, practice and more practice. This set doesn't come naturally to most people and takes work to master.