I'm creating a game with a lot of elements. Should I store all components that I'll eventually access on class variables (memory) or should I access them when running the script(processor)?

Example:

private SpriteRenderer sprite;

void Start () {
   sprite = GetComponent<SpriteRenderer>();
}

public void StartMovement()
{
    sprite.doSomething();
}

VS

void Start () {

}

public void StartMovement()
{
    GetComponent<SpriteRenderer>().doSomething();
}