Rolling method "Observed (member)"

Hello Community I would like to know in what form, the "Observed (member)" method determines which node will deliver the load.

In my scenario I have several ClearPass Clusters, of different capacities, in different geographical locations, and for the http and https services, we are evaluating the use of a VS that balances the load, we want the traffic to be sent to the less congested node and I believe that the Rolling method mentioned in the title, would be the most appropriate. Could you advise me please?

Thank you.