Questions about GridMove

I understand how GridMove works, but I had two questions regarding it's structure that I don't quite understand:

Why is there an implementation of…

 transform.forward = Vector3.Normalize(new Vector3(Input.GetAxis("Horizontal"), 0f, Input.GetAxis("Vertical")));

Unless it is a fallback for the later interpolation method that is used. Normalizing the vector3 with only x and z used would be entirely 'horizontal' format dependent grid, and also the fact that transform.forward

And what is the math behind

 tx = 1 - 1.0 ; 

to reduce hiccups in the math calculated by t a few lines above?

Just curiosity. Thanks!