Performance appraisal is actually done periodically, usually yearly- in organizations to assess their employees. For performing the same, recording of their works will be done on a monthly basis.
It actually measures the performance of the employee and suggests improvements and setting targets for him. In most of appraisals the ultimate result will end up with a salary hike, depending on the performance of the employee and the band under which he will fall after the appraisals.
Also there is chance for a position change based on the review or the recommendation of the respective manager. So in one or other way, an appraisal does help employees a lot and in most cases employees will be awaiting for the appraisals and results.