I take supplemental calcium to strengthen my bones. With an inability to consume much dairy, and the importance of calcium in combating osteoporosis, calcium supplements are a necessity for me.
But, life is never that simple. Calcium must be supported by other vitamins and minerals to work properly. For example, supplemental calcium depletes the body's stores of magnesium.  Therefore, magnesium may need to be added as a nutritional supplement when calcium is involved. When deciding how much calcium and magnesium to take, most sites recommend a ratio of 2:1 So, if a person takes 1,000 mg of calcium, he/she would need about 500 mg of magnesium. 
Vitamin K2 is also needed, when calcium is taken, in order to direct the mineral into the bones, rather than allowing it to take up residence in the arteries. (For more on this, see blog post #2 on Vitamin K2.)
Finally, Vitamin D is necessary for the body to absorb supplemental calcium.  There is no point in taking any vitamin or mineral if the body cannot absorb it.
The benefits of calcium supplementation, as well as contraindications, are outlined in an excellent article on the mayoclinic.org site.  Please visit the site below!
Timing considerations are also important. For example, some articles suggest that magnesium and calcium should not be taken at the same time.  They are both minerals, and they compete with each other for absorption.  But, for me, there are not enough time slots to separate these minerals. I take a liquid combination calcium/magnesium/Vitamin D supplement daily.
Most forms of calcium need to be taken with a meal. But, calcium citrate can be taken with or without food. It is recommended for people like me who have low stomach acid. 
Vitamin D and Vitamin K2 are both fat soluble. These vitamins must be consumed with a meal containing some fat in order to be absorbed effectively. I take Vitamins D and K2 MK-7 in the morning with breakfast (a meal containing 35 g of fat). Refer to the blog post #11 My Typical Daily Food Diary detailing the fats I am referencing.
There are even more limitations surrounding calcium supplementation. According to Consumer Labs , people should not consume more than 1,000 mg of supplemental calcium per day. Also, it should be noted that a maximum of 500 mg of calcium can be absorbed at a time. Therefore, a greater dose of this supplement would need to be divided over the course of the day.
Proper calcium supplementation is vital for those of us with bone concerns. Research demonstrates that 1,000 mg of calcium paired with 400 iu of Vitamin D works to reduce fractures of women who are on hormone replacement therapy due to hysterectomies. 
As you can see, decisions regarding supplementation can be a bit tricky. Much research needs to considered before adding any vitamin or mineral supplements to the diet. And, each person's doctor should be consulted prior to starting any supplement regimen.
ConsumerLab.com information is available for members. I have a subscription to this site, and I recommend it for anyone who is taking supplements. The information is unbiased, paid for by subscribers, and not influenced by manufacturers of supplements.