he needs to make a proper base for himself or a base of commands that could be moved as his troop is going to the place where they can find the soul healing item, and to set up the sword essence formation again this time with even more essence that he has learned. i can see zuo mou figuring out to make those secret realms that people like for storage sake however he doesn't need them for cultivation as him and most of his troops have those formations branded onto them that auto gather ling power for them
Never said it would be for cultivation. I figured it would be for forging resources and trade. He's got a lot of non-combatants that need a way to justify their presence, which requires resources for them to use.