Board Thread:Theories and Speculation/@comment-31099706-20180126164032/@comment-734582-20180126173508

Seems to me that he was simply intended to be an additional pawn in case he needed more firepower. His plan during the Gokage summit was to have Sasuke weaken the Hokage in the hopes that he could then negotiate on more favorable terms. As Obito noted, that failed.

He didn't need Sasuke explicitly, but Obito did note that Akatsuki was low on firepower. So yea, i don't think the plan was anything more complicated than "use him in case i need more soldiers".