In general, statistical accuracy increases with the square root of sample size. Doubling your sensitivity and accuracy quadruples your cost. It's a power law, not a normal distribution, and it pushes us toward extremes.
In measuring soil carbon using traditional sampling, what this means is that the high achievers are easiest and cheapest to measure (circled red in the diagram below). A sampling scheme that is adequate for measuring a large change in soil carbon between an initial baseline and resampling, may not yield a significant result if the change turns out to be small.