Coprophagy (copro = excrement, dung; phagy = one that eats) in reptiles is not well documented on the exact reasons why some herps will eat feces. An old theory was the belief
a need to eat the feces in order to establish their gut bacteria, and that they would not be able to eat food until they do so. However, hatchling tortoises, like other oviparous reptiles continue to live off the remains of their yolk sac for at least a week after they hatch, during which time they will take little, if any, other food. The coprophagous tendencies of sulcatas is well known to sulcata keepers who also have dogs; if left to do so, some sulcatas would cheerfully clean up their yard of all dog feces.
Now the bad …..The most obvious risk is that the feces ingested may contain parasites looking for a new host. Once the feces is ingested, the parasites will have found a new home. In reptiles eating the feces of other taxa, such as tortoises eating dog feces, the risk of disease transmission may be low, but there is still a goodly number of zoonotic diseases that may be transferred this way.Salmonella, of course, can be transferred this way. One tortoise keeper I know lost most of her hatchlings when she "inoculate" the hatchlings with the feces of one of her apparently healthy adults. It turned out that the adult had more Salmonella than the immature immune systems of the baby torts could cope with.
Frye, FL. 1991. Reptiles: An atlas of diseases and treatment. TFH, Neptune City, NJ.