For ER shadowing which I've done, it's essentially following around a doctor for roughly 4-7 hours on their shift. Often at the end of the shift, the doctor is dictating summaries of cases, which doesn't offer much of benefit.
The point is to learn what an MD really does. Often, shadowing is done for maybe 15-30 hours or less, it's considered better to shadow different specialties rather than shaow one MD for much longer.
It often takes some time to get to know an MD well enough for them to allow one to shadow them, although there are exceptions. I think this is because the MD is volunteering a portion of their attention to teaching a potential future medical person, which would pull some of their attention away from the patient.
It was helpful for me to see things from the doctor's perspective - I'd volunteered for well over 100 hrs in the ER prior to shadowing, and had seen quite a bit from the RN/EMT perspective, but, logically, an MD looks at things quite differently.
Many MD US schools consider shadowing helpful or required to be considered for admission, although this is not written anywhere that I could find; I learned it by asking admission committees at different schools what they valued. There are some med schools, however, that feel it has NO value; I'd suggest shadowing in addition to other clinical volunteer work.
Med schools in general are looking for clinical experiences that expose the prospective student to how medicine really is in practice; this involves patient contact and observation of the md/patient interaction.
