A recommendation letter is a potential gift for a valued employee

A recommendation letter plays a specific role in the world of Human Resources and employment. It's occasionally needed, but never preferred. Employers would rather speak directly with the former supervisors of their prospective employees.

However, employers realize that direct communication is not always possible - hence the importance of the recommendation letter.

Employees lose track of supervisors when they move, change jobs, or retire. Businesses move and close or are merged or acquired. Human Resources departments lose records. Even employees who make the effort to stay in touch with a prior supervisor as a potential reference, and prepare their references for a reference check, can lose track of their supporters over time.

A recommendation letter lasts forever and its contents may not apply years after the recommendation letter is written.
 
Writing a Recommendation letter:
A recommendation letter can last forever and is a snapshot of an employee’s performance at a certain moment in time. Consequently, give thought and care to how you write a recommendation letter and to the information that your recommendation letter conveys.
 
What not to include in a Recommendation letter:

• Details that you may not know for sure if they were outside of the confines of the employee’s employment with your firm.
• Prediction of the future.
• Personal, protected, or confidential personnel information of any kind.
• Anything other than factual information that you can directly, with personal experience, report.

A recommendation letter can save the day. Written on company stationery, with a clearly printed address and telephone, the recommendation letter provides a sometimes needed boost to an applicant’s credentials.

As an employer, particularly if you anticipate changes … do your exiting employees a favor. Supply the employee with a recommendation letter.

A few more details can be found in this article.