Future stuff. I think comes with 2nd anniversary, you will be able to use them to acquire MP(Master Point) which are used for unlocking new EXes for each soul & you will also be able to distribute them to give each soul new passives with each soul having their specific passive trees. You don't exactly have to go out of your way to farm SPs coz you won't be using them all, but make sure to exchange the leftovers.
On a side note, MP can also be gained with exp, but requires a shit ton of exp.