Baking blind is to bake a pie shell empty of any contents in it, to harden and dry it. You do this for this pies whose contents — such as Lemon Meringue — wouldn’t stand up to the full cooking time required for the crust. So you give the crust a head start. It is also done for pies whose contents would be too soggy to allow the crust to fully cook without that head start.
Foodies usually recommend that you bake the empty pie shell with something in it to weigh the bottom down to ensure that it doesn’t rise or puff. Usually, dried beans, ceramic baking beans, dried lentils or baking marbles are recommended.
Many people, though, have never found it necessary to use the weights, and feel the last thing they need in their lives is a bunch of ceramic beans clanging for a storage spot somewhere in the kitchen. To bake an empty shell without much ado, just poke the bottom and sides liberally all over with fork pricks, and then bake.
If you really feel you want to use weights to bake blind with (though rest assured, the fork-pricking works fine: ask generations of housewives), then treat yourself to the ceramic beans, or put them on your suggested gift list the next time your birthday rolls round. That way, you won’t have to waste real beans or lentils. Even though you can re-use the beans or lentils a few times, you wouldn’t want to for very long as eventually they’d get a bit iffy from picking up fat from the crusts; and it may be better if you at least have something ceramic that you can toss in the dishwasher and sterilize properly.
Baking blind in Roman and medieval times was always done with just the pie crust on its own. Adding beans, rice or ceramic baubles is a modern practice.