Supplements are best used in situations where an individual is unable to get their nutrients from their diet. Perhaps an individual has an allergy or intolerance, for example lactose. They are unable to consume milk products which in turn limits their ability to get sufficient calcium and vitamin D from their diet. In that case, a supplement makes sense.
A systemic review on human interventions makes note of a study conducted on patients of osteoarthritis (Edelman et al. 2000; cannot be located online) which found improvements in joint pain symptoms relative to baseline in the Velvet Antler group and not placebo, although a lack of information on blinding and randomization precludes results that can be drawn from this study.