What is the difference between a probationary employee and a permanent employee?

There are several differences between permanent and probationary employees from both the perspectives of the employee and their employer. For instance, permanent employees participate in retirement plans while probationary employees do not. But, the crucial difference between the two classes of employees which drives this appeal is that it is much more difficult to terminate a permanent employee than it is to fire an employee on probation. (See Birdsall v. Carrillo (1991) 231 Cal.App.3d 1426, 1431, 282 Cal.Rptr. 504 ["A probationary employee serves at the pleasure of the County and may be rejected from a position without a hearing or judicially cognizable good cause" (fn. omitted) ].)