I've had good success with my quilts being nice and flat after piecing them.
I make sure that the borders are even - I mark them at block intervals so if it's necessary to do a little easing of the main body in, it comes out pretty well.
I try to layer them carefully before quilting them - I've had to repin a few times when I had puckers on the back.
I use the big square on the corners and long rulers (48 inch) to try to get the top laying nicely on the batting and backing. And pat and tug and nudge to get it laying nice at this point.
Then I quilt them.
They are usually okay at this point, but I will trim any stray threads - shaving a few edges here and there -
After binding them, I machine wash and dry them. They turn out nice and flat.
My answer is, No, I don't block.