We provide a comparison between overlay Device-to-Device (D2D) and cellular communications in TDD (Time Division Duplex) wireless networks using queuing theory. For that, we provide a theoretical analysis of the queuing stability region of two wireless network models: the first one is a pure cellular network where any two users (UEs) can communicate with each other only through the Base Station (BS) and the second one is a hybrid network where D2D communications are overlaid with cellular communications. The communications that pass through the BS involve a coupling between the queues of the network due to the relaying functionality at the BS level. Hence, applying a queuing theory approach allows us to capture this coupling. In this paper, we investigate the stability region for both scenarios and we derive new insights on the cases where overlay D2D outperforms cellular communications. Furthermore, numerical results are presented to corroborate our claims and demonstrate the gains that overlay D2D can bring to cellular networks.