If you’re deficient and the form of the vitamin/mineral is something your body can absorb, supplements can be helpful. If you aren’t deficient, some supplements have little effect (water soluble ones just get peed out, though can cause wear and tear on your kidneys and/or liver in the meantime), while others can cause overloads which can be as bad as or worse than deficiencies.

Personally, I try to meet my micronutritional needs with foods but I occasionally take supplements to “top up”, either a multivitamin if there’s no specific signs of deficiency, or specific supplements if there’s signs I might be low in that one (each has a set of symptoms that are associated with deficiency).