One could use the same argument, that screeners read hundreds of descriptions, to mean that one should write their own such that it stands out a bit. Not by being flamboyant, of course, but perhaps by including a bit of humor or by touching on how the activity affected you or something interesting you saw or learned. My eyes would glaze right over "Shadowed Dr. Smith in his clinic for 50 hours as he saw patients," but might be interested in "Shadowed Dr. Smith for 50 hours as he saw patients, including seeing cases of childhood diseases I had thought were essentially wiped out such as scarlet fever," etc. You want to be unique, not simply cover all your check-boxes.