Some are beneficial, many are just a scam. Lax regulations have brought us a plethora of noisily marketed food supplements, which promise to deal with all kind of health-related and cosmetic problems.
In these posts, I put the scientific validity of those claims to the test:
Should you take DHA during pregnancy? – Jan. 2018
Sulforaphane. Curing cancer with broccholi? – July 2018