That doesn't really make sense to me, to be honest. I know that many medical students think that doing anesthesia during CBY gives them an advantage. IMO it's a waste of valuable internship time, unless the interns are allowed to function as CA-1s, with all the pressure and responsibilities that come with that.
The value of a CBY should lie in the opportunity of doing both medical and surgical (mostly the former) useful rotations, plus electives. Many medical students, who go into anesthesia because they hate both medicine and "clinic", don't realize that they will be the internists in the OR (and possibly outside). Surgical rotations are much less valuable, except for monkey skills, and that's the main reason they should be done. There are very few surgeons who can teach an up-to-date evidence-based approach to fixing medical problems. As an anesthesiologist, one will treat co-existing medical diseases (or the medical aspects of the surgical disease); the surgical ones will not be your responsibility.
Just my 2 cents, regardless of the program.