If you are making a sampler quilt or any project with blocks or units that are not all the same, you do need an accurate 1/4". It's not going to work to just say all the seam allowances are the same. Why? Because a block with 10 seams will shrink or grow by twice as much as a block with 5 seams. Candace is right that the thread, fabric, pressing, and initial seam allowance all affect the finished size of your block. And don't forget the cutting! To me fretting over the 1/4" seam makes more sense than stretching blocks and dealing with puckers and wavy borders later. Getting back into quiltmaking after several years with very little production, mostly quilting tops made previously, I find I'm practically back at square one