I DON'T always square-up! It depends on the quilt. However, if you are using precuts it is wise to check your blocks after construction to make sure they are all the same size. Sometimes the pre-cuts aren't always perfectly square. Anything that has bias edges you should most certainly square the blocks. Some of it has to do with how good you are at pressing, how accurate you are at cutting, and how consistent your 1/4" seams are. All these steps in the quilting process can make a difference in the size of each block. Right now I'm making a quilt by an Eleanor Burns pattern. I used the "Shape Cut Pro" to cut out my strips. It makes for extremely accurate and consistent strips for piecing. If you're not familiar with it check out a demo on U-tube! Also if you try as much as you can to sew your patches together so the grain is going in the same direction on each piece in the block that can make piecing them together a lot easier. If you've got the give in the grain going in one direction and the next piece is going in the straight-of-grain direction they won't always fit together as well.