There are many ways to measure success; how do you know you are successful as you lead your family, Cub Scout troop or Fortune 100 company? Lord Kelvin stated, "when you can measure what you are speaking about, and express it in numbers, you know something about it." Each leader has a style where they are comfortable and have found success. Most often, it will be borne out of personality and experience of what they have seen works. Some experiences will provide negative training, and the leader will commit to running their organization directly opposite of their experience. Paying attention to the numbers can help understand your leadership effectiveness.
A friend was discussing his job transition into a new field and took a significant pay cut to right-size his work/life balance. His last company would grind through managers at a rate of three per year after demanding 100 hour weeks at the job and sparse vacation days. The union labor force was competent and stable, allowing for managers to be overworked, quit when exhausted and quickly replaced. Leadership had determined that these managers were expendable for the short-term gains. I mentioned that even with the pay cut, his hourly rate probably skyrocketed due to the normalized hours at the new job where he was finding great satisfaction.
As a leader of people, your responsibility goes beyond the easy metric of units produced, dollars collected and the least amount of time spent with each customer. Your investment in those you lead will pay dividends beyond the basic spreadsheet. Like any investment, you want to understand your returns. Lord Kelvin's statement reminds us that once we can quantify what is important then we "know something about it"; so, what do you know about your people?
Going Further: Other than required company metrics, what do you use? How do you track the success of those you have led? How do you know that you are not a negative learning experience for your people? What else should be asked?