Is "transform.position._" an expensive call?

I mean; does it spend any significant amount of processing time when I look up the transform component of the object the script is on?

Ought I to declare;

xPos = transform.position.x;
yPos = transform.position.y;
zPos = transform.position.z;

at the start of any function where I will be using position information more than twice, and then use the variable xPos instead of writing out transform.position.x?

Or is this really the same thing except for the time it takes to type it out, and assigning variables is a waste for this purpose?

Regarding to this video it is an expensive call:

Unite '07 Presentation - Performance Optimization

The best and simplest thing to do is not have separate xPos, yPos, and zPos variables, and just use a Vector3 like transform.position does. Then do "`pos = transform.position;`". Things like .transform aren't really "expensive" at this point (it's been optimized compared to what it used to be), but it's still better to cache it in a variable if you're going to use it a lot.