What is the motivation behind building reversible logic gates ???
As,every node can be generalized as a capacitance that would undergo charging/discharging depending upon the inputs and the logic that that particular gate has been designed to realize. And every node would dissipate charge in form of leakage power.
What if someone takes the output and feeds it back to the inputs forming a "Positive Feedback" structure! In order words, one can sustain the inputs from outputs and outputs would anyway be dependent on inputs.
Doing so can save a lot of leakage power and this exactly is the motivation behind building reversible logic gates.
It might be easier to appreciate the advantage of such a logic gate when many of them are attached in cascade as shown below. Here the output of one gate would sustain it's input which, in turn, would be the output of some other logic gate and it would continue on forever!!