Lead Passing:
Lead passing is used to place the ball on a certain spot of the field when passing the ball. Lead passing is performed by simply pressing the button of the WR you wish to throw to and then leading the ball in whichever direction you wish by pressing the direction by either using the directional pad or analog stick. If you hold down the WR's icon, you will throw a bullet pass, but if you tap the WR's icon, you will throw a lob pass.
Lead passing is ideal for routes in which you want to gain separation from the defender covering your offensive player. Streaks, corner routes, drag routes, and fade routes are all example of routes that I tend to prefer using lead passing on. I would say, I use lead passing about 90 percent of the time when I want to click onto the WR and catch the ball myself.
Precision Passing:
Precision passing is used to place the ball on a spot of the WR you are throwing the ball to. For example, you can place the ball high to make the WR have to jump for the ball or low which will make the WR have to dive for the ball. You could also place it to the left or right of the WR, but I do not recommend using precision passing in this instance as it is risky and can lead to picks. If you want to place the ball to the left or right of a WR, I recommend using lead passing so you place the ball in a spot which only the WR can get to.
Precision passing is performed almost exactly the same as lead passing. The only difference between the two is that when you want to perform precision passing, you need to hold down the left trigger as well. You can still either throw a lob or bullet when using precision passing based on whether you tap or hold down the WR's icon who you throw the ball to.
I only recommend using precision passing up. Precision passing up is used to trigger SPC catch animations and also the rocket catch animation. By placing the ball high, you can make the WR have to go high up in the air to get the pass, which will trigger these animations on certain routes.
Note the Spectacular Catch animation
You can trigger these animations on most routes, but some of the better routes to use this tactic on are wheel (fade), corner, angled streak, and curl routes. If you wait until the WR turns around on the curl route, and use precision passing with pass lead up, you can trigger the rocket catch animation without having to click on and perform it yourself.
Final Thoughts:
When it comes to precision passing, player ratings are important. To trigger the SPC animations, you will need a WR with a SPC weapon if you play on all-pro, but if you play on all-madden, any WR with a SPC rating over 84 can perform it. However, WR's with higher SPC ratings will be much more consistent getting the animation on a wider variety of routes than WR's with lower SPC ratings. When it comes to the curl routes that trigger the rocket catch animation, the SPC rating is pretty much useless. Any WR can perform this animation, however WR's who are tall and have good jump ratings will be the most effective as they can catch the ball over multiple defenders.