I frequently wash and block something I am knitting while it is still on the needles. I do this when I am concerned about how my project is coming out. Something doesn't look right, and I don't want to go farther until I am reassured that all is OK.
My Catkin Shawl was a good example. The 'corners' of this shawl use lots of slip stitches to create the graphic stripes. The 3 corners looked a bit weird on the needles, but once I started binding off, I realized that they were curling and twisting oddly. The image below shows the shawl unblocked, still on the needles (see them on the right?).