Well, some vitamin supplements are fat soluble, and some are water soluble. Water soluble vitamins, Bs, C, are flushed straight out of you body (once enough has been used) via kidneys, and bladder. So, expensive pee. Fat soluble, need fat to be broken down to be useful to the body, so very low fat diets e.g will be lacking. Fat soluble vitamins are A, D, E, K; there may be others, but I am not an expert (retired RN), and they are stored in the liver and released as needed. So, it can be dangerous to take more than recommended.
Herbs - I generally just use in cooking, and I have no knowledge of how a herbalist works.
Minerals - again, the body takes what is needed from food/diet. Problems arise with some illnesses and the absorption of minerals; e.g, kidney disease and potassium, many cancers and calcium, some breathing problem and magnesium.
Pharmacists - in the UK anyway - tend to have an exhaustive knowledge of compatibility within medicines and OTC supplements, and will always advise.
I was a Nurse Practitioner with a nurse prescribing qualification. By the time I had completed my prescribing course, I was almost frightened to prescribe anything! That did settle though. I feel that if a person is well and active, then there should not be any need for supplements, and constant self medicating with minerals, vitamins and other supplements, is only making the manufacturer richer.
I take one multivitamin with added iron daily, when I remember, but only because I am a blood donor, and being vegetarian it prevents a wasted journey, if my blood count is just below their cut off point.