As someone who struggles with Candida, I occasionally include egg shells in my diet as a calcium supplement as per the anti-candida diet of Bee Wilder. Basically, wash, dry and grind egg shells to a fine powder. Mix with freshly squeezed lemon juice and soak for 3+ hours. Apparently, this forms Calcium Citrate which is a highly absorbable form of Calcium. It's not something I do regularly, however.
With the exclusion of dairy products and minimal amounts of vegetables, nuts, seeds etc in my RAF diet I am concerned about Calcium intake. I find this supplement helps if I begin suffering with insomnia.