Harvest-use (HU) is an energy harvesting (EH) architecture where the received energy cannot be stored and immediately must be consumed in order to maintain operability. Due to its current limited application interest, this architecture has not yet been examined in the literature and its deployment to communication system is an open problem. This paper deals with the application of HU architecture to communication systems and investigates cooperative protocols where the relay node has HU capabilities. We show that HU relaying introduces a trade-off between EH time and relaying (data communication) time; this trade-off is discussed for two fundamental relaying policies a) Amplify-and-forward (AF) with half-duplex (HD) relaying and b) AF with full-duplex (FD) relaying. The optimal time split is formulated as an optimization problem and an approximation is given in a closed form. Numerical results show that FD outperforms HD and is introduced as an efficient relaying policy for HU cooperative systems.