Trumping your partners ace is tactic that when properly used is not only helpful if you are trying to euchre the opponents. There will be times when it is the only way to turn a one-point hand into a two pointer. There may also be circumstances where it could save your team from a euchre.
The dealer sits in the South position. The score is 7 to 6, North/South team's favor. West passes and North orders the dealer to pick-up the 10 of spades.
West seat starts the hand by leading the ace of clubs. The maker(N) trumps in with the queen of spades. East follows suit with the queen and South throws off the queen of diamonds. For their next lead, the maker(N) chooses the right. This lead pulls out three trump. Now a total of four trump have been played.
Now the maker(N) leads the ace of diamonds. East follows suit with the king. It's now South's turn. He looks at his hand and realizes he holds the top two trump. There is only one left in the wild. Not willing to risk that it may be in West's hand, he trumps his partner with his ace, then leads the left. This assures all trump are accounted for. Now leading the ace of hearts gives his team two points and closer to a win. The score is now 9 - 6 (and with a block on the next hand) North/South are now in a position to win. If South had not trumped his partner's ace West would have made their king good. This could have changed the outcome of the game.
Knowing when would be the correct time to trump your partner's ace only comes with experience. If you choose the correct time you are a hero, if you don't, well, let's hope you have an understanding partner.