Here are reasons that you should look at supplements/vitamins:

1. Medicines can only be prescribed after an extensive series of tests, which can take 10 to 15 years. This costs money and since there is no financial benefit to doing so pharma companies prefer to research new medications for which they can patent and gain financial benefit from.
2. In certain countries healthcare is prohibitively expensive so supplements might help.
3. In other countries people there are large delays in healthcare, so you might want to try something to alleviate your symptoms whilst you await treatment
4. Conventional medical treatment might not be working for you, so alternatives might benefit you.
5. You have a family history of certain conditions, so you want to see if there is anything that can prevent you suffering the same fate.
6. You have certain symptoms but not enough for a diagnosis. Could supplements alleviate your symptoms?
7. You want to be as healthy as you can.
8. You have found a supplement which has helped you and you want to share the knowledge.
9. Many supplements are generally regarded as safe by millions of users.
10. Preliminary Studies (some linked from this website) do seem to show a benefit.

Here are reasons why you might be cautious:

1. Supplements may interact with existing medications that you are taking.
2. Some supplements do have side-effects.
3. Supplements don't go through the same rigorous testing as medications.
4. Quality of supplements may vary between companies.
5. Some vitamins (B6 and B12) have been linked to increased risk of cancers.