An experienced blackjack player knows that when they have two aces, they have a high-percentage hand. If the dealer has two aces, it is also in their best interest to give you a good hand.
In blackjack, the house edge is 1.5%, so for every $100 you bet, the casino will make $5 on average.
So, if you are dealt two aces and the dealer also has two aces, the casino will give you $100 back and still make $5 on the original bet.
This is why experienced blackjack players know to try and get two aces whenever they can.