I don't sew completed blocks until I have all blocks completed. There are times I have one block that's too small. Or I don't want to end up having the same fabric touch from 2 different blocks. Sometimes I get sew happy and end up having a lot more extra and make the quilt bigger and have enough left over for a pillow case. Usually the smaller ones end up there. That's ok though, because I'm not keeping it...out of sight, out of mind.
I was taught in a quilting 101 course to sew my quilts in columns. I've recently changed my ways because of the quilters on this board. If instead you sew a quilt in 4 sections; right upper corner, left upper corner, right lower corner, and left lower corner, you will only have to sew one long seam versus many long ones when sewing one column to the next and so on. Get it? If you sew the corners together first, then sew the top pieces together, and the bottom corners together...then you only have one long seam (the width seam) to sew when joining the top and the bottom together!!! Short seams go quicker!!! I promise!