Question about Vector creation

If this has been asked before I’m sorry, I couldn’t figure out what to type in google to find the answer!

I have the option of either creating a named Vector at the top of my code class with something like:

          Vector3 myVector = new Vector3( 0, 0, 4.0f);

…and then using/updating this vector to a different value as needed in a method such as the update method like;

void Update ()
{
	transform.position += myVector;
}

or I could not create that named vector at the top and inside one of my methods I could do something like this:

void Update ()
{
	transform.position += new Vector3(normalSpeed, 0, 0);
}

…which seemingly creates like a “throwaway” vector that’s not named and presumably discarded.

I’m interested to know; what are the considerations/differences? Should I always use the named Vector method where possible to save memory? If so, why do a lot of tutorials use the “throwaway” method?

My wild guess is that if you’re going to use the vector only once, do the throwaway version as you don’t need to store a variable that you’ll use once.