Most IT people that I know would plan to run between 50-70% CPU utilization. Any greater than that and it is time to order more servers. I don’t have specific numbers, but I know from experience that the more cars and trucks that are on the highway, the slower it takes me to get to where I am going. The fact is, with processing data in a CPU, or processing cars on a highway – the delay increases exponentially as it nears 100% capacity.
So if you wouldn’t run your servers at 100% capacity and we don’t plan to have our roads at 100% capacity, why do we expect to run our human resources at 100% (or greater) capacity? Fact is, we are in a dynamic business with customer requests surfacing often and unpredictably. If we have not built slack into our organizations, we have not prepared them to be responsive to our customers.
In his book on Slack, Tom Demarco indicates that having slack in an organization gives it the capacity to change, to reinvent itself, and to marshal resources for growth. Mary Poppendieck in Lean Software Development has a whole chapter devoted to queuing theory and the relationship between capacity, batch size (another blog at another time) and cycle time.
In practice, I have found that innovation, quality, efficiency, productivity and responsiveness are all related to a teams utilization. Leave a team some slack and your team and customers will thank you.