Teach your employee something that expands his (oer her) current job description. Teach something that will help him to get promoted within your organization at a later date. Teach him a skill that uses new technology. Or, teach him something that will allow him to be a more skilled leader and manager in the future.
You can even teach something that you no longer need to be doing in your position, but that will be a rewarding challenge/task for your employee.
The benefit to your employee is obvious. The benefit to you is you'll have a more skilled team member who is capable of handling more work that can help you to grow your business and/or make it run more efficiently.