Chromium is an essential trace mineral needed in only small amounts. Good sources include meat, nuts and cereal grains, and vegetables such as broccoli contain some too. Most people can get all the chromium they need by eating a varied and balanced diet.
Chromium contributes to the maintenance of normal blood glucose levels. That authorised role is why it often appears in formulas designed around balanced energy and blood sugar. It is not a substitute for medical care or prescribed medicine if you have diabetes.
In supplements, chromium usually appears as chromium picolinate or chromium chloride, with the amount of chromium itself listed in micrograms (µg). Research on chromium is still developing, and the NIH notes that while chromium from food and supplements does not appear to cause harm, the research is limited. That is a good reason to stick to the amount on the label and to count chromium from every product you take.