Generally, the more data you have, the closer your results will be to reality and there will be better confidence in the results. As a rule of thumb, you should generate at least 15 operator 'ranges' in the GRR Study for a minimum level of statistical confidence in the results. From the Range-average calculation sheet, you will observe that each operator generates one range for each part for his/her trials. So with 5 parts, 2 operators and 3 trials, 10 ranges are generated. With 10x3x3 scheme, 30 ranges are generated.
To quote from the manual:
As with any statistical technique, the larger the sample size, the less sampling variation and less resultant risk will be present.
Hope this helps..