Doing the math isn't the issue, marking the project is. How does one accurately mark 4 71/128ths or 4. 5546875 in multiples consistently and why would you? It's simpler to pick a number like 5" TTW for side walling then diagonal your tape from point a to b and mark 5s. The average homeowner can't see it, (a blur to their eyes) but a trained pro can see a 1/4" difference in a course height change. 1/16ths and 1/8ths, as long as the changes are maintained around a house are invisible to everything but a tape measure or transit.
Never bite the hand that looks dirty!
The more you know the more you're worth