A book I have on Russian tortoises says this:
"Occasionally you might see your tortoise consume its own feces. While this might be an unpleasant sight, this is mentioned here because it is a common practice among tortoises and is thought to be an important part of tortoise nutrition. If you remember, the Russian tortoise is a hindgut fermenter, and many nutrients are wasted because of this. It is suspected that consuming its own feces, called coprophagy, is a means of reducing the waste of available nutrients. It is like running the food through the digestive process a second time to absorb those nutrients made available when the material was broken down the first time around. Tortoises of many species will even consume the feces of other animals, both in nature and in captivity."
