One of the best ways to hold on to your best employees is to give them appraisals or benefits for their outstanding performance. This is the most important aspect of employee performance management for supervisors. This is also what exactly Google did to prevent its top guns from joining Facebook. Lots of employers today, offer performance reviews to appraise the work of existing employees. Performance reviews give evidence to an employer, who can then conclude if an employee will get an increase, a promotion or a bonus. A poor performance review can cause the termination of employee's job.