It is almost NEVER +EV to hedge a bet.

The only time is when you want to 'take a position' on a game beforehand.

Say Team D +7 is +101 now. You're sure that you'll be able to get a better price on Team C -7 (same game) later.

So teams A and B win and Team C is up. But LOOKIE! Team C is now -7 (+118) or even -6.5 (-101)! NOW It's +EV to hedge.

But really, if you don't have enough confidence in a game to let your parlay ride out, you shouldn't include it in your parlay.

Otherwise, all you're doing is eating juice at both ends of your last game in order to do hold what you would have held if you hadn't included that last team at all.