If you have a healthy diet, supplements should not be required unless you have a diagnosed condition. On the other hand, for the vast majority of supplements out there, there probably isn't any harm in taking them in moderation, so if you have the spare cash to burn and it makes you 'happy' then why not?
As an example, I do not medically need any supplements. However, a friend recommended marine collagen to make my hair grow thicker. My beard has always been a bit thin and whispy, not exactly a problem (medical or otherwise) but certainly a situation that has been improved by the marine collagen supplements, so I continue to take them.
Vitamin D could be a good for certain people during winter. I personally have gone for installing UV lamps in some parts of my house so my body can continue to make VitD naturally, and I happen to like the aesthetic effect. If I didn't, I'd probably just take the supplements.
I also take cod liver oil for joint recovery after playing sports. Seems to help.