Some programs require a "chairman's letter", so you'd better have one on-hand.
I don't know which school you attend, but at many schools this letter is a formality and is constructed in the form of a MadLib. Actually, I heard a story of a guy confronted at an interview when the interviewer asked the guy why he was consistently referred-to in his chairman's letter as "she". Clearly, a personal touch would be nice, but most chairmen are trying to help their students get spots, so I wouldn't worry about it too much.
In other words, the letter may not help you but it almost certainly won't hurt you... except for another story I heard of a guy who got called from a program upon receiving his application to inform him that one of his LoRs stated: "he will make a great orthopaedic resident, just not here". Oh well.
