In so many airlines now it's computerised (in my company's case, laptop/toughbook) anyway so there is no noticeable trimsheest design as such.
That's exactly why operators can say effectively 'bung in the numbers, check them, and look at the result'.
The original question I believe referred to exactly what many guys have answered. Having done the first bit as described above the trim part does not need to be recalculated until a certain limit is reached (either total or in an individual hold) because that falls in with the error factor allowed.
I don't see anyone here suggesting that it should be the same for everyone or every type - now that would be nonsense!