All this gets you to a basic die result number. This can be a significant step. The time spent on these add up so the more you have, the longer it takes. With respect to math, addition is the fastest. Subtraction and small multiplications are the next best.
Division is, by far, the worst.
In generally, you should try to stick with addition only if you can. The other major mathematical consideration is the size of the numbers you are dealing with. Most people can quickly add numbers below ten and fairly easily add numbers up to 20 or 30. Double digits, of course, take more time. Subtraction and multiplication become more of a problem in double digits and should be avoided.