There are several reasons for mutual termination involving employee and company. In some cases the employee makes the decision and informs the employer.
In other cases, termination may be a result of a mutual decision between employee and employer.
Depending on the circumstances, some companies may ask for an exit interview from employees who are voluntarily terminating. This information can be used to the employer's advantage for making improvements in the area of employee retention.
Employees who are transferred to a new location leave present employers for new jobs. The transfer can be due to a promotion by the company or another business division of the parent company. When employees move, they may know in advance that they are leaving and can give their present employers a notice (maybe two weeks). If the employee has been a value to that division, eligibility for rehire may be available should the employee move back into the area.
Sometimes an employer may offer an opportunity for the employee to voluntarily resign. This could be a result of personality clashes, a mismatch between employee and position, or due to a poor performance issue where the employee has made an honest effort to improve without success. Some employers may feel that the employee is not a bad person, but rather not a match for the specific environment.
Employees may leave employers due to mergers or acquisitions of the company.
This termination may be mutual in that neither the employer and employee have any control over the situation. Some of the time, employers may offer severance (continuance of salary) for a period of time. This separation is due to financial situations rather than performance issues.