Cardiac resynchronization therapy (CRT) has proven a very useful tool to treat heart failure (HF). In HF patients with severely depressed left ventricular dysfunction and ventricular dyssynchrony who remain symptomatic despite optimal medical therapy, the "reverse remodeling" induced by CRT leads to a significant improvement of survival and quality of life. The addition of the cardioversion-defibrillation function to CRT (CRT-D) is considered a further beneficial effect to reduce overall mortality secondary to a decrease in sudden death rate. Unfortunately, the amount of this additional benefit is still uncertain; in particular, how much the cardioversion-defibrillation function contributes to prolong patient survival remains to be elucidated. Such uncertainty leads to a different therapeutic approach to HF patients, i.e., an extended or restricted use of CRT-D devices. Even the most recent guidelines do not provide a clear answer to this question. The present review summarizes the current evidence regarding efficacy, effectiveness, safety, and cost-effectiveness of CRT and CRT-D, and suggests some practical solutions to the appropriate use of CRT-D on the basis of clinical, ethical and socio-economic considerations.