Every manager has a few go-to employees who take on any special project thrown at them.

But if your go-to employees have too much on their plates, they will not be productive. In fact, they won't be able to do their day jobs, let alone the extra work you have them tackle.

Ron Ashkenas, a managing partner of Schaffer Consulting, writes in Harvard Business Review about the problem of overtaxing your reliable lieutenants. "Managers sometimes 'round up the usual suspects' because they only trust a small number of people to handle key projects or initiatives. Every organization has its 'glue people,' the ones who don't show up in organization charts but are assigned to every task force or initiative because they are respected and trusted," he writes.

But if you draft the same overworked group every time to handle new business challenges, you won't get any results. "These task force members usually end up with multiple specialty assignments piled on top of their regular duties," Ashkenas writes. "And because these few go-to people are spread so thin, they ultimately don't accomplish all that much."

Ashkenas has simple advice: Stop overusing your usual suspects. If you don't have more capable, loyal, and trustworthy employees, then something is wrong. As a leader, you need to give employees chances to take on challenges and stretch to their potential.

"Most organizations have ambitious agendas that are limited by the availability of key people. There may indeed be times when calling upon a few trusted people is the right approach, but doing it too often can be severely constraining," he says. "That's why thinking outside the roster of 'usual suspects' can help you distribute responsibilities in a more even, efficient way."