It is necessary to submit a letter of resignation when you leave your present job. The letter of resignation should be written in a polite and discreet language. The language used should reflect maturity and professionalism. Remember, writing resignation doesn't mean that you are getting fully cut off from the present employer or it doesn't mean that you will not need his favor or a recommendation letter from him in future. You may need a favor or recommendation from your present boss in future, therefore, show discretion, respect to him while tendering resignation.