Final answer:
Slits in a pie crust are used to let steam escape and prevent the crust from bubbling up, ensuring even cooking and a well-structured pie.
Step-by-step explanation:
Slits are cut in the top crust near the center of a two-crust pie primarily for letting steam escape during baking. If steam is trapped under the crust, it can cause the crust to puff up or bubble, which may lead to an unevenly cooked pie. While the slits can also be decorative, their main function is practical. When steam escapes, it prevents the build-up of pressure inside the pie, ensuring the integrity of the pie's structure and appearance after it's baked. This allows for the filling to cook properly without affecting the crust negatively.