A risk factor of not getting enough calcium is problems related to weak bones. This relates to children not reaching full potential adult height and adults having low bone mass which is a risk for osteoporosis.
Calcium is a highly-researched supplement with several benefits. Like all supplements, consult your doctor before consuming.
Calcium is crucial for bone health, and also belongs on any good guide to supplements. Choose to take a calcium supplement if you can't get enough through your diet.