Chariklo...unfortunately, it is not about how effective the "preaching" work is, but rather it becomes a yard stick to determine how spiritual an individual JW is. If you don't make your hours, it is assumed you are spiritually weak. It is very unlikely you will be appointed an MS or Elder if you don't maintain a minimum number of hours. I guarantee that is a hot topic when the CO visits and evaluates current and future servants.
So much for tracking effectiveness...