Why do pie crust recipes tell you to refrigerate the dough before rolling it out?
Refrigerating the dough after mixing has two main benefits. First, it cools down the fat, usually butter and/or shortening, making it firm again. If the fat becomes too soft, it will mix too completely with the flour. To get a good crust, you need small bits of solid fat layered into the dough. Re-solidifying the fat makes it roll into chips rather without blending it further into the flour.
Second, the resting period allows any gluten that was formed during mixing to relax. This makes it easier to roll the dough and contributes to a softer, flakier texture.
Also, if during rolling the dough starts to spring back too much, it may help to refrigerate it again. Put it on a cookie sheet between two layers of waxed paper or parchment paper and refrigerate for another half hour.