Job performance evaluations should motivate employees to want to improve. They should also make employees aware of any concerns a manager has about their job performance. Overall, I believe people want to do better and improve, and a job performance evaluation is a formal way of giving employees the regular feedback they need on their individual performance. Performance evaluations should be given at least once a year, as a basis for raises or lack thereof. You should consider doing them for all employees prior to layoffs or downsizing, so that employees do not have the defense "my last review was excellent!"