We're not gonna suddenly become a boss attacking unit, but his movement and close control ensures that chances fall to him, and the ball stays alive in the box. Plus, Coutinho needs a striker making clever runs in order to perform to his best, and Balotelli is frankly a fucking idiot when it comes to attacking movement. He either runs offside, he doesn't run at all, or he runs in the wrong direction.
And he's just someone who can occupy 2 defenders at once. At the moment, Balotelli is being easily marked by a single player, leaving an extra defender to congest the edge of the box at all times. You can't really leave 1 centreback on Sturridge though, since he does a bit of everything. Runs off the back, drops for the ball, shifts to either wing. He's too much for 1 player to track for 90 minutes