Function Start vs Function Update

Questions & Answers
1

I was looking at a pong tutorial online and I noticed that If I put the boarders for the game inside of function update, then they would overlap each other and THEN readjust, so the ball would hit both colliders and you would have one point for each player. So I changed function Start to function Update and then the Player(the pong bars) would not readjust with the camera like its supposed to with ScreenToWorldPoint. So why is this. Why can’t I just put the have “Player01.position.x = mainCam.ScreenToWorldPoint()” inside function Start()?

function Start () 
{	
	topWall.size = new Vector2 (mainCam.ScreenToWorldPoint (new Vector3 (Screen.width *2, 0f, 0f)).x, 1f); 
	topWall.center = new Vector2(0f, mainCam.ScreenToWorldPoint(new Vector3 (0f, Screen.height, 0f)).y + .5f);
	
	bottomWall.size = new Vector2 (mainCam.ScreenToWorldPoint (new Vector3 (Screen.width * 2f, 0f, 0f)).x, 1f); 
	bottomWall.center = new Vector2(0f, mainCam.ScreenToWorldPoint(new Vector3 (0f, 0f, 0f)).y - .5f);		  
	
	leftWall.size = new Vector2 (1f, mainCam.ScreenToWorldPoint (new Vector3 (0f, Screen.height * 2f, 0f)).y); 
	leftWall.center = new Vector2(mainCam.ScreenToWorldPoint(new Vector3 (0f, 0f, 0f)).x - .5f, 0f);		
	
	rightWall.size = new Vector2 (1f, mainCam.ScreenToWorldPoint (new Vector3 (0f, Screen.height * 2f, 0f)).y); 
	rightWall.center = new Vector2(mainCam.ScreenToWorldPoint(new Vector3 (Screen.width, 0f, 0f)).x + .5f, 0f);
}
	
function Update ()
{	
	Player01.position.x = mainCam.ScreenToWorldPoint (new Vector3 (75f, 0f, 0f)).x;
	Player02.position.x = mainCam.ScreenToWorldPoint (new Vector3 (Screen.width - 75f, 0f, 0f)).x;
}
2

Start only gets called once at the beginning of the script it is never called again, so it’s only useful for initialization not for setting values that will need to change over the lifetime of the script. So I’m assuming there is something happening elsewhere that causes the player’s x to change causing the need for the x position to be set every frame.