Hedging = to prevent complete loss of a bet by betting an additional amount against the original bet.
If the pick-3 ticket cost is low enough and the payoff is high, I will look to hedge. Usually I would be looking to hedge just in the 3rd leg. I will hedge anytime I see an opportunity. Ideally we'd be looking to guarantee a profit regardless the outcome of the race.
For example, let's say we are live in the 3rd leg with probable pays on 2 horses of $75 and $100. Let's say it's a 9-horse field and we're only worried about 4 other horses beating our pick-3 ticket (original cost $10).
We can look to structure a hedge like:
#1 (5-2) $10 win (will pay $35)
#2 (5-1) $6 win (will pay $36)
#3 (8-1) $4 win (will pay $36)
#4 (8-1) $4 win (will pay $36)
So now all bets total $34 and we've virtually eliminated risk of loss by betting against our pick-3 will pays, which now are $41 ($75-$34) and $66 ($100-$34) net.
So if our pick-3 cost is low enough and we already know probable payoff will be high, we can start hedging in the 2nd leg against any horse that we think can beat our ticket. An 8-combo 50-cent pick-3 for $4 is easy to hedge in the 2nd leg and increase likelyhood of profit should we get beat. A few $2 win tickets should more than suffice.
Anytime I structure a pick-3 I'm automatically trying to set up a hedging opportunity in the 3rd leg.
Hope this clarifies.