This may seem like a good thing to do. But by tilting your head down to look at the ground. You bring your center of balance forward, and you bend your body. As you come down into a landing, the curve of your body ends up absorbing some of the shock your springs desperately needed to send you flying just a bit higher.
It's true that you need to be aware of your surroundings. But look with your eyes, and not your head. Always try to look about 20 feet or so ahead of you. This will keep your body up straight, and not shift your balance.
This is a vital skill to get down, it really helps you out. Even if it doesn't seem like it would. For instance, if I look down at the ground, jump and try to do a Split Kick Double Grab, I can get my hand to my toe, but not my other hand to my back spring. BUT when I look up and forward, I'm able to grab my toe, and grasp my back spring. Little things DO matter!