For me, if you're playing Bournemouth, you play him where ever you think will benefit his development most, if you're playing Juventus away, in a very important game, you play him where he best suits the team.
My reaction to my lad, when he replaced Sergio, was "game over". We'd given up any chance of scoring in that moment, and that is not to knock Sterling, its to knock the manager, Both his outfield subs tonight were baffling. Until the first one, I thought we had the shape, to get something, possibly even a win, from the game and had played pretty well, after the first sub we were clueless, lost any drive we had, and the second just cemented it. I'm often moaned at for being a Pellegrini lover (I often stand up for him), tonight he got the starting line up spot on, I was pleased with it, given the injuries, and so it proved, bar another unfortunate goal, poor poor team defending.
In the second half he got it wrong, and he gave us no chance from the minute Fernandhino was taken off.