I was told in a class that starching made it easier to machine quilt the blocks when completed. I've washed, dried, ironed and starched all of my material prior to cutting to get a good cut, make it easier to match up the pieces, and iron seams open after stitching them together.
It does seem to make a quilt come together more easily. Cotton so easily wrinkles that a starched piece holds a finger press much easier (and you can use the line created with a finger press as a stitching guide on an intricate pattern). It gets washed away when the quilt is completed and cleaned.
Pretty much it's personal choice.