I don't run this game (yet), but on my current casual playthrough of the US PS1 version on Duckstation, I came across a potential minor time save for the Ultima Weapon fight.
This sounds like a prank, but - if you use the soft reset right after the fight where you finally defeat Ultima Weapon (i.e. R1 + R2 + L1 + L2 + select + start), it actually skips the 10~ second animation of him crashing to the ground. [I found this because Tifa died during the fight and I wanted her to get EXP.]
I've only tested this on emulator, although it would be weird if console behaves differently. While this is a pretty minor time save, especially for the two categories it's relevant to - All Bosses and 100%, as far as I know - the real significance is it raises the possibility of soft-resets having similar effects in other parts of the run.
Finally, sorry if this is already known, but I did look at the WRs for All Bosses and 100% (console and PC) and didn't see it being performed. Maybe it's too minor for people to risk accidentally soft-resetting over. But I figured better to share than not.
EDIT: Sorry if there's ads on the vod, not my choice, it got copyright claimed over the battle music.