Infinite Elixers

[Karifean]

I don't quite get it - does the enemy attack have to land and kill everyone before you hit retry? And does it have to interrupt the usage of the elixir?
Also, wtf use a potion on Hope? Doesn't a potion simply heal everybody?
Also, why is speed so important? And the party setup?

Edit: Okay just discovered the source through Google:
Link
That answered most of my questions... except for why the hell you need so much speed. Does he think you can only use items with a full ATB gauge?