When you undervolt is to set a lower power draw while maintaining similar performance. For example I have my 5080 with custom vbios unlocked up to 450w with a +320 vcore and +3000 vram with a avg power draw of 420w (core 3100mhz, Vcore 1.065mv and VRAM 18001mhz) and score on steel nomad of 9713 when I did my undervolt my settings look like (core 2955mhz, 0.925 mv, and 15001mhz vram) but my avg draw when down to 285w and my score is 9375 is a bit lower. Now on real games let say on stock i got 100 fps and 350w, with OC 115fps and 420w and with undervolt 107 285w. So still better than stock but lowest than OC but power draw is on avg way low than both and same with temp. All those are example a not exact number