Calibration plots and reseaux are used to ensure that the table is in good order. If your map is much larger than your table, you will have problems trying to take the digitized pieces and knit them together into a coherent map. Also, a large table can have the operator stretching to the distant parts, with the potential for introducing parallax errors. Operator accuracy, precision, experience and state Operators have different levels of accuracy and precision in their work. Part of the operator effect is experience.
More experienced operators tend to produce better results.
However, an operator's state also affects how data is collected. In addition, some less experienced operators can degrade the quality of their data by the way that they deal with it.