Blocking works for every unit of the quilt, from a strip, as you posted here, to an unfinished unit that didn't quite measure up or completed block that was just shy of being the full size, to the entire finished quilt. With completed quilts I only block if I intend to show it because it hangs so much better.
Once I participated in a block swap and chose a PP pattern. Well the pattern must have been off just the tiniest bit as my 12 1/2" Unfinished blocks were consistently measuring 12 3/8. Because they were for a block swap I needed them to measure the full 12 1/2 so I blocked them and it worked great.