Although the surrogate may understand at first the details of the surrogacy contract she signs with the intended parents, the fact that she's the biological mother of the child may make it difficult for her to relinquish the child after giving birth.
This is considered the major con of traditional surrogacy, contrary to what happens with gestational surrogacy, where she is not genetically linked to the child. This may make it easier for her to relinquish the baby in favor of the commissioning parents. For this reason, straight surrogacy arrangements have fallen into disuse nowadays.
On the other hand, from a technical standpoint, traditional surrogacy involves a simpler medical process than host surrogacy. Since the surrogate is inseminated artificially through IUI, it is not required that she undergoes medical treatments prior to the procedure.