Why is my forward and backward movement slower when aiming at ground in FPS template?

I have a question as to why all of math is necessary here.

Why multiply by one in beginning? Why clamp float down at bottom?

It’s working, and thankyou! But I’m curious as to WHY.

My assumption is that clamping is for restricting where camera can look, but I don’t know why this setup works > this one.

http://puu.sh/i3Rdp/59c0a9a1f1.jpg