Putting him in the middle also removed one of our most deadly attacks. When he's on the right, defenders heads naturally turn to him permitting Neymar or Alba to quickly run in behind, prompting him to do that beautiful right to left crossed pass that he perfected last season. From the middle he still managed to do some initiating lobbed passes, but they were generally too telegraphed and easy to read.
Also, generally speaking, a lot of our attacks start with Messi getting the ball somewhere on the right side, and then the attacking movement of the team sort of naturally flows from right to left. It has become part of the attacking rhythm and pattern that makes MSN so effective. Placing him in the middle did confuse his teammates a bit, and it was especially evident with Suarez. Many times their positioning got awkward and their movements was not in sync.