OIML R60 classes run from A to D, with C subdivided into C1 to C10 by the number of verification intervals. It is natural to specify the best class available, but the class only sets the cell contribution to the error budget.
What the class covers
For a C3 cell the maximum permissible error is 0.023% of capacity per verification interval at the first interval, and the cell must hold linearity, hysteresis, creep and temperature effects within limits derived from that. A C2 cell has half the resolution, which is still far better than most mechanical installations deliver.
The rest of the budget
Add the indicator resolution, the reference weight uncertainty, the mechanical structure and the temperature effect over the actual working range. In a typical hopper installation the structure contributes more than the difference between C2 and C3. Buying C3 while ignoring a pipe restraint is spending money in the wrong place.
Where class matters
Trade weighing, where the legal requirement fixes the class, and any application where the cell is the dominant error term because the mechanics are good and the environment is controlled. In those cases going up a class is the cheapest accuracy available.
Kevin Huang