Some populations have greater variability than others. For example, we would expect greater variability in the weights of dogs at a dog park than at a beagle meetup.
Dog park:
Mean weight: 12.8 kg MAD: 2.3 kg
Beagle meetup:
Mean weight: 10.1 kg MAD: 0.8 kg
The lower MAD indicates that there is less variability in the weights of the beagles. We would expect that the mean weight from a sample that is randomly selected from a group of beagles will provide a more accurate estimate of the mean weight of all the beagles than a sample of the same size from the dogs at the dog park.
In general, if samples from a population have similar sizes, a sample with less variability is more likely to have a mean that is close to the population mean.