Residual renal function (RRF) contributes to the achievement of treatment adequacy in CKD-5 patients. It may facilitate patients' acceptance of renal replacement therapy (RRT) in minimizing dietary and fluid restriction. It has been confirmed to improve dialysis patient outcomes. Attempts to preserve RKF in incident CKD-5 patients are still subject to controversies. In this review we analyze the role of RRT in dialysis patient. What are the positive and the beneficial effects of maintaining RRF? What are the negative and the risks of maintaining a RRF? At what expense the maintenance of RRF is achieved? Preservation of RRF is undoubtedly an interesting means to enhance the efficacy of renal replacement therapy and reduce dietary fluid restriction. However, maintainance of RRF should not be considered as a goal of dialysis adequacy in dialysis patients but rather a means of optimizing RRT. Further, preservation of RRF should be considered as a permanent trade-off between patient comfort and chronic fluid volume overload with its deleterious effects.