Exactly! I have also seen (I think) Jenny Doan use a 2.5" strip and cut with scissors to the size of the square it's then attached to AFTER stitching. I have done this a few times and, if you aren't constructing a large size quilt, it works out OK especially if you have a very good eye and can cut straight. But it doesn't take much time to cut the strip to 8.5" and 12.5" pieces before sewing and that makes your outcome more certain.
Attach the two short sides and press. Then attach the long sides and press. Great for chain piecing! Figure out on floor, bed, or design wall what block arrangement suits you. Sew all together.
NOTE: By alternating the short and long sides you avoid having to "nest" the short side seams and avoid bulk when quilting. Since you are looking at the front and the overall design when you are deciding where to put the blocks, you may not think so much about seams. After you decide what your best block overall layout is, check on these short side seams "living" next to each other. UNLESS you are using a directional (has a top and bottom to it) center block, a simple 90 degree turn of abutting short sides will eliminate bulk. HOWEVER, if you don't think of this, it won't matter much in the greater scheme of things. I just like to eliminate seams crossing seams where I have a choice. My machine can handle these bumps but she's becoming an old gal like me and I like to look out for her.