Most efficient scope of declaring variables

Would using variables that are used every frame be more efficient if they are declared once globally or is declaring them every frame acceptable?

For example we use a Vector3 for some calculations every frame.

Case 1-

Vector3 vector;
void Update()
{
    vector = //Some Calculation
}

Case 2-

void Update()
{
    Vector3 vector = //Some Calculation
}

Case 2 is undeniably cleaner and preferable but with publishing to mobile in mind would declaring a number of variables each frame have a noticeable impact on performance?

Thanks in advance

performance isn’t usually an issue - best practice is to declare variables close to where they’re used. if you’ve got a variable only used within a method/function, then declare it locally within it rather than globally.

typical use to the contrary is when you’re caching things which are unlikely to change for expensive (in cpu) operations such as GetComponent() where you’d perform it once in Awake()/Start()

you’ll have less issues with conflicting variables, etc. later on…