Sharon Schamber has several videos on Youtube about how to do this when you have a "wonky" block. The purpose is to straighten the block so it can be accurately sewn to other blocks in the quilt top, and so the quilt top will lie flat for sandwiching. If you were to wash the block before it was quilted, it would revert to its distorted shape. However, once it is quilted (at least moderate quilting -- not lines 10" apart), the batting is stronger than the fabric and will keep the fabric from going back to its unstraightened condition.