It seems rather pointless if you have actual clinical experience (such as EMT work) and you have volunteered in a hospital. If medical schools look for someone who has something that they can add to their medical education that the medical school would not provide, then why would shadowing a doctor for any amount of time be of any importance at all?
You are right to be skeptical. You’ll hear a lot of opinions from people who really don’t have a clue what they’re talking about. Most of these opinions are along the lines of “My best friend’s second cousin’s sister went to medical school and this is what she said.”
Admission committees like to see applicants have some exposure to a health care environment for two reasons: demonstrate a sincere compassion for health care and to dispel the myth of Hollywood’s version of health care.
If you have EMT experience you have no need to do any volunteer work.