Altar 9 slots upgrade

Hi there, I just unlocked the 9 slots for offering, but I don't really get the point of having 9 slots since every soul is offered 1 by 1.

Even for prepping for event, 4 slots for 48h souls was very Ok to get the bonus ( only downside was the lost of the last day Daily Quest, so it's fine now with 9 slots ).

Am I missing something? Are you guys prepping for more than 4x48 ?