What is the difference between Magnitude and divided by half?

For making things clear:

What is the difference between divided /2 or getting the Magnitude?

and for what do people use Vector3.new(0,0,{-}direction.Magnitude)

I know what is direction, I know what is Magnitude, and I know what is a Vector and a Cframe.

But I cant understand some properties.

Magnitude and dividing by 2 isn’t the same. One is getting magnitude, one is halving (not dividing by half :P)

To get a Vector3 with positive or negative magnitude of a direction (which is generally just 1, since it’s direction) on the Z, likely for sizing/positioning.