I definitely see undervolting becoming the new overclocking. Boost algorithms are getting so good these days there's not many gains to be had with overclocking. However, these algorithms are based on things like voltage, amperage, and temperature - if they hit a threshold they scale back. So by undervolting, you scale back on both voltage and temperatures, meaning there's actually the potential to get a slight performance increase. Realistically probably like 1-2%, but it's still a nice to have considering you're actually extending the chips lifespan by doing this.
Voltage, heat and current degrades silicone, so by lowering these two energies you slow the degradation process. Even at stock settings, degradation happens, just at a slow enough rate that the manufacturers reckon you'd have upgraded before it happens anyway.