Letters of recommendation are poor substitutes for references. With few exceptions, they are all likely to read the same—“Sally is one of the best employees and finest individuals it has been my privilege to know”—and consequently do not carry much weight with employers. There is no substitute for direct contact with a reference.
There are, however, circumstances when a letter of recommendation may be unavoidable. It may be the best endorsement you can get if you leave an employer in poor standing who subsequently refuses to serve as a reference. However, be warned: employers are not necessarily deterred from contacting the letter writer. Moreover, in this suspicious age, signatures on letters of recommendation are usually impossible to verify. Employers, especially those who employ Ronald Reagan’s mantra when negotiating nuclear weapons reduction treaties with the Soviet Union—“trust, but verify—tend to discount completely a letter of recommendation because they cannot be certain that you did not write it yourself.
The only other time a letter of recommendation might be of some value is if the writer states that a prospective employer should feel free to contact him or her for additional information about you…in other words, a situation where trust can be verified.