Is there a difference between double quoting a variable or a whole line in echo

When you type, for example,

echo Variable "$var" is not initialised.

and

echo "Variable $var is not initialised."

the front end result is the exact same (as far as I know, at least). But I was wondering, from echo's perspective, if there are any difference on how the command is ran.

And performance-wise, is the latter faster, since echo would recieve all arguments at once?