I would argue that there is no one answer that is correct.
First, we should look at how the answer might differ based on the employee. If an employee has been doing a really good job over a number of years, it is likely that that employee should only be evaluated once each year. The firm already knows that the employee is a good and productive employee and so evaluating him or her on a quarterly basis would simply be a waste of time and money. By contrast, if a firm evaluates someone who has been struggling on a quarterly basis, it would not be a waste.
Second, we should look at the purpose of these evaluations. If the evaluations are only for the purpose of deciding who should get promoted or given a raise, or put on probation, then the evaluations should be conducted annually. This saves on money and time and it also puts less stress on employees. Furthermore, it gives employees time to correct their mistakes and improve their performance. If, however, the evaluations are meant to make the firm run more smoothly, more frequent evaluations are warranted. Performance assessments can be used simply to make sure that the firm is running efficiently and that employees know what is expected of them. Frequent assessments of this sort can be very useful as they provide a more continuous look at the functioning of the firm. This is better than only getting the information once a year.