what difference between Update and fix Update ?

I saw the difference between them and I know the difference between them

fix Update to sync frame

But in this case I will put all the codes from Update to fix Update it good for me! sync frame

so why not put all code to fix Update why we need Update?

does fix Update Is consumed by the processor and memory?

FixedUpdate is called every physics tick. It could be called multiple times in a frame or not at all. It’s meant to be used for physics calculations.

Update is called each frame and is really the best place to do no physics calcs and operations so things match with the frame times/speed.