You should only hedge if:

1. You think the hedge bet is +EV on its own.
2. You overbet the original side and need to reduce your exposure for bankroll considerations.
3. You stand to win a life-altering amount of money (this usually only applies to contests, 100-1 futures, game shows, etc.)

Hedging with a -EV or even neutral EV bet reduces variance at the expense of also reducing EV. Since the goal for most bettors is to maximize EV (while maintaining an appropriate risk of ruin), you do not want to voluntarily give away your EV by hedging for the sake of hedging.