  The rate and energy efficiency of wireless channels can be improved by
deploying software-controlled metasurfaces to reflect signals from the source
to the destination, especially when the direct path is weak. While previous
works mainly optimized the reflections, this letter compares the new technology
with classic decode-and-forward (DF) relaying. The main observation is that
very high rates and/or large metasurfaces are needed to outperform DF relaying,
both in terms of minimizing the total transmit power and maximizing the energy
efficiency, which also includes the dissipation in the transceiver hardware.
