It's always seemed very pointless and just doesn't fit well with this game. Considering you can't actually choose the episode you want to play without a save file at the start of it. And there arent enough save slots to save at the start of every episode. And not to mention the episodes are so short all of the IL'S would be optimised within a couple of days.

Raid mode has variety, campaign doesn't and having them both on the same board would be a cluster fuck