Air leaking from the AC system into unconditioned space will result in air being pulled into conditioned space from outside to make up for the loss of air. It will just seep in from the points of least resistance such as doors, windows and voids in the building structure. The air will drag in whatever heat, moisture, pollen, dust and other pollutants it comes across. I'd suggest sealing that leak, every little bit adds up. A duct leak of 15% of the conditioned air will result in a 25% higher energy consumption for cooling and heating.
“I am for doing good to the poor, but...I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. I observed...that the more public provisions were made for the poor, the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer.”
― Benjamin Franklin