I prewash my fabrics but I still always wash the quilts when completed. As others have said, removes starch; smells; dog hair; oils from my hands and the crinkly look. And even though I prewash, I've had fabric bleed after completion. What a nightmare that quilt was. No matter how many color catchers I used it wouldn't stop bleeding. Finally gifted the quilt with a box of color catchers and instructions to never wash it without them.