In the 4-3-2-1 point count, an ace has a value of four points, a jack one point — supposedly to reflect their trick-taking power.
I can't say whether aces win four times as many tricks as jacks, but aces are potent cards. An ace is a control and an entry, but it is worth full value when it promotes the value of accompanying honors.
Today's South holds "aces and spaces": He has no secondary honors for his aces to promote and no intermediates. The worth of his hand may depend on what fillers North can provide. But most Souths would count their points and open 1NT because opening one diamond would leave an awkward second bid if North responded in a major.
When South arrives at 3NT, West leads the jack of hearts. South counts eight tricks and might get one more from spades or diamonds.
Among its virtues, an ace is a winner that may be taken at a player's discretion. And since South needs a count of the East-West distribution, he can take advantage of being able to score his aces when he chooses. He wins the first heart in dummy and leads a diamond: jack, deuce, queen. If West shifts to the queen and then the jack of clubs, South ducks.
West shifts back to hearts, and South wins, noting East's discard. South then ducks another diamond, wins East's diamond return, and takes the ace of clubs.