Red Brinstar Fireflea Room
For the Hero Shot to break the top block, you can just do a single jump to follow it up, as opposed to without Hi-Jump which requires multiple quick walljumps.
This video shows the fastest RTA-viable climb at the start of the game:
You can get past the third ripper without waiting, but it requires incredibly tight walljumps, and isn't considered RTA-viable:
The lower walljump shown in the KPDR section is in the logic of most randomizers, so you will be expected to be able to go back up once you have Hi-Jump, Ice Beam, or Morph Ball and Bombs.